What matters most is response time. There is the occasional game that requires fast response times or the game won't run properly.....Castlevania PoR is one of the most prominent. It requires a response time of 0.7ms or better so as not to lock up all the time. The fastest microSD I have only has a response time of 0.8ms. And I have many different ones.

If you think class can sometimes be hard to determine, response time is something almost none of the microSD's ever give a spec on. It's something you have to test for yourself, of course at that point, you already bought the microSD. A program called HDtach will test for response time.

Another thing about most microSD's, they tend to read the info faster than they write it. A program I use is called ATTO Benchmark, it will report both read AND write speeds, whereas HDTach does not report write speeds....on the flip side, ATTO does not report response times, which is why I use both to determine all microSD speeds.

THEN, there is a remote possibility that the microSD you buy won't be liked by the CycloDS. I've had this happen first hand. The same exact brand worked for some and not for others......it happens, just be aware of that.

Buying a microSD is a crapshoot. There are recommended brands, but their specs can float from batch to batch and there's always a chance you'll get a defective one, so individual results of any test will vary from unit to unit.

My advice to you is, stick to the popular brands, go with what is recommended and hope that when you get it, it actually works as you hoped.

As for Class, shoot for Class 4 or higher.