to reinforce estel's comment, i have a 64gb sdxc class 10 uhs-1 card, formatted on device (have to reinsert to make it appear in file manager). partition 2+3 are 1gb swap, 1 is vfat. no issues what so ever since i started using it with kp51r1.

if your using ext4, i would look at tuning it during format. can't remember exact param but is something like -O^has_journal. this will disable journal, which although not quite as good for data integrity is usually much better for sd performance.