That would be fine. SDXC spec goes to 104MB/s vs 10MB/s for microSDHC. 100MB/s transfers from storage on a portable would kick ass!
Usability is more important to me than portability...
I don't know where you read that but there's nothing in the protocol that differentiates transfer speed capability between SD and microSD (both come in SDXC variants). They're electrically identical. You can buy microSD cards today that can read up to 95 MB/s, and you'd probably have a hard time even finding ones that are capped at 10 MB/s...
You know, this sort of thing comes up so much despite all the posts we make decrying it (even in this very thread!), maybe we should just put it in the FAQ or something.