You'd do better getting a dedicated USB drive. Wii is USB2.0 but I'd not worry about class as on the Wii you'll not really notice a benefit.
Hey, im about to buy a new 16gb for my wii (for playing backups of gamecube games mostly)
And i just came to think of, which brand is the best to use? Or is it the same which i use?
and can wii read up to 10-12MB's of a class 10?
Ok, but doesn't a sdcard for gamecube games work better for gamecube iso's?
Or was that the sdcards it worked best on?
You can USB load GameCube games as well.
I have a 32gig class 10 card (bought it before USB loading of gamecube games was viable) and it works well.
We still recommend using a 2gig SD card for the modding, but once it's been modded, the larger card up to 32gigs will work.
Sandisk branded is the best overall cards in terms of quality and compatibility.