So I just got a 128GB and 256GB card. I have an old Galaxy Tab that only supports the 128GB but my new Note 9 supports the full 256GB card and higher. In any case the prices of these cards have dropped so much that I finally decided to spring to replace my 64 and 32GB cards that I have in my Note and Tablet.
First things first - you always should run h2testw on your cards to test read / write to be sure there are no errors. I do a couple of passes, let it write and verify one round, then delete the files it creates and do another round. Every now and then you will get a card that has errors that you want to pick up before you start using it.
The very first thing I noticed was the 128GB card was getting 70 MB/s writes but the 256GB was only getting 37MB/s writes. I had the test running on two computers with the 256GB running in a newer system. Once the testing was done on the 128GB card I swapped the 256GB to the other computer and my speeds went up to 70 MB/s. That's good - I was going to return the card.
Either way for the newer pricing (March 2019) these cards are so worth their money for how fast they are. Maybe if I had a newer laptop I could get faster speeds. For reference I was hitting 70 MB/s writes on a laptop that had only a 2nd generation i5 CPU so it is hovering at 6-7 years old. The computer that could only push 37 MB/s has a 6th gen i7 and it's only 3 years old but the built in card reader must be slower or attached to a slower interface than the much older laptop.