I went with a SanDisk SDXC UHS-I in 64GB for my 2520. I formatted it as exFAT since this is what was recommended by the card management utility.
Here is how it tested out with
h2testw:
Formatted exFAT
Test finished without errors.
Writing speed: 13.1 MByte/s
Reading speed: 35.2 MByte/s
That said... I recently got one of these Samsung SDHC UHS-I in 32GB to use in my 1520 and it has a great write speed:
Amazon.com: Samsung 32GB EVO Class 10 Micro SDHC Card with Adapter up to 48MB/s (MB-MP32DA/AM): Computers & Accessories
Here is the same test:
Formatted exFAT
Test finished without errors.
Writing speed: 18.8 MByte/s
Reading speed: 35.3 MByte/s
Fastest write speed out of all the cards I own and have tested recently. Why not give the Samsung a try?