Those numbers seem very high. USB 2.0's theoretical maximum is 480Mb/s. Does the Slim have USB 3.0 ports?I think as long as it supports 70MB/s reads and 40 MB/s writes you should be OK.
Beware of the really cheap, really slow drives. I almost bought a SanDisk Cruzer on Black Friday (I think it was 32GB for $10), but the reviews were universally awful.I realized that at least as of this writing despite 32GB support Microsoft doesn't have any "official" drives anyway, so I'll grab one off amazon.
I think as long as it supports 70MB/s reads and 40 MB/s writes you should be OK.