The Artisan model has a larger mixing bowl (5qt) with a handle on it, and a larger motor 350watts. Easier to use than the Classic due to the ergonomics of the bowl, less motor strain when mixing heavy doughs or large batches.
I thought discussion was between "Artisan" and "Classic", not "Pro".... But in any case, I have had a "Classic" for about 15 years now, and my Wife just bought me an "Artisan" to take to Florida with us since we've become "snow birds" this year for the first time. And I turned them both on and the Classic definitely spins at a noticeably faster speed on all settings including the fastest speed setting, whereas the Artisan spins slower. I don't know about "when under load", but if you were whipping egg whites or cream, where the load is very low, I would expect that the old "Classic" would whip them faster on the basis of my "test" above.
From a chat with a KitchenAid rep on 1/9/14: The motor in the 5 quart Artisan is 325 watts so it can handle 9 cups of all purpose flour while the 4.5 quart Classic Plus stand mixer has a less powerful motor so it can only handle 8 cups of all purpose flour. The 4.5 quart stand mixer has a 275 watt motor. They both have a combination of metal and nylon gears, but it is the same combo. The attachments are universal so they will fit all KA stand mixers regardless of age or model. The bowls are considered accessories and those need to be specific to each model, but the tilt head mixers such as the 4.5 and 5 quart mixers have interchangeable accessories. The bowls can be used between the two.
OK, this isn't exactly true. Input wattage does have significance. First let's talk about what watts are with respect to power. 746 watts = one horsepower (HP). For example a motor, any motor regardless of what it is driving, with an input power of 250 watts is considered approximately one third HP (250/746=~1/3HP). The difference between input power and output power is the efficiency of the motor. So if we have a motor that is rated at 200 watts input and puts out 100 watts we can calculate that the motor has an efficiency of 50%. (100/200 x 100 = 50% efficiency). To find the efficiency of the complete machine we must take into account all the losses so let's say our mixer has 5 gears that give up 20% in efficiency. We have to subtract that from the total working efficiency. What's important is if two machines both have an efficiency of 50% for instance, and one has a 400 watt motor and one has a 200 watt motor then the more powerful motor (400 watts) will give us approximately twice the power to do real work. This is the significance of power in our kitchen machine regardless whether it is a blender, an electric can opener or whatever. Now here's the rub, a machine can have lower efficiency but make up for it in a more powerful motor as we can see from the above example. Efficiency does not necessarily mean a poorer design. More gears would decrease the efficiency but give us more working power at a slower speed for instance. What is equally as important as power is how well motors and machines are made. Two motors can have the same power but one might use a higher temperature wire in the armature of the motor. This translates to an ability to handle greater loads which generate greater heat. I don't know how well the motor on new KA machines are made but from looking at the specs between the Artisan and the pro models I'd say the pro is a much more robust machine and not just from the power ratings. The pro will knead 12 cups of flour where the Artisan will only do 9. That's a significant amount. The pro also has steel gears as opposed to plastic in the Artisan. I'd say the pro will knead bread all day long but the Artisan might not. If all you do is light work then the Artisan will get you through but don't expect it to be the bullet proof product the old KA mixers were. Which machine would I buy? The pro.
Wattage is not important to measure the performance of a stand mixer. It is important if your basis to choose a stand mixer is its power consumption. Input wattage is simply the power that flows from the electrical outlet into the mixer's motor. Output wattage is the amount of power the motor actually produces--which flows out of the motor, moves through the mixer arm, and, ultimately, smacks the ingredients around. Most mixers list input wattage, which is simply the power that flows from the electrical outlet into the mixer's motor.
Reference: America's Test Kitchen Review 11/205 What does input wattage tell you about the power of a mixer? Absolutely nothing--it's purely a marketing gimmick. To wit, the six models that failed the bread dough test (our initial round) had power ratings ranging from low to high, mostly high (275, 350, 400, 450, 700, 700). In addition, every other test showed absolutely no correlation between mixer performance and wattage. (If manufacturers were willing to provide output wattage figures, comparison would be easy, but this key bit of data is never offered.)
I have a Classic Plus model, 275 watts. I was doing a little research, I think the main differance is the motor, the bowl, and the color options. I haven't used an Artisan personaly but I have bought a 5 quart bowl with the handle that comes with the Artisan and use it in my Classic Plus. It works just fine. My wife makes big batches of cutout cookies every year and it boggs down a bit with that kind of load, but that things a tank, it just takes it and asks for more!
Don't buy either, IMHO. I wanted one for years and finally bought an Artisan, though I only use them for family dinners.
On its 5th or 6th use, it dumped grease oil in the food. Just sitting, it started dripping oil, and the gears started sounding distressed.
KitchenAid support said this is normal. They said I should run the mixer every couple weeks. On average, over 3 calls to customer support, they indicated it was normal for the gear grease to separate and drip into food.
Liz, I can only tell you about the one I bought - Kitchen Aid Artisan (tilt head). I love it!! It fits under my kitchen counter while their bowl lifts don't. I've had mine a little over a year. My mother had a Sunbeam stand mixer when I was little but when she passed away, it was not working at all. I would have loved to use it. After seeing my friend's Kitchen Aid, I knew I wanted one. The Artisan has 325 watts and comes in about 25 colors. The Classic (to my knowledge) only comes in Black, White or Red and has 275 watts. Ktchen Aid also has the bowl lift models, and some come with more wattage and different size bowls.
There are people on here who know a lot more than I do. I hope someone can give you more info than I can.
My only suggestion to you is to do some research and go shopping! See them in person...any brand you can find and take a close look. See what comes with them and if you can buy attachments later on if you want to. If you like any of the home shopping shows, see what they offer, too. And of course, as always Amazon has a great assortment of probably every mixer on the planet. Good luck!
I have a Kitchenaid mixer which I purchased in 1971, yes, 1971, paid $93.00 for it and it STILL works. In those days, this was an investment as I had just gotten married. I guess it would be considered to be the Classic Plus. In these days, it just was a simple Kitchenaid mixer and that is it. At that time, still made in America by Hobart, as was my Kitchenaid dishwasher. Now stuff is made in China, sadly. Added a pasta attachment and meat grinder. It still works wonderfully. Also, bought a glass bowl which recently came on the market. It works great. Take care of things and they will last a lifetime. I am 73 years old now and am still enjoying it. Get Kitchenaid if you want the best.