I don't know....I have a Class-6 64gig card in my Rezound and skipping to the next song is nearly instantaneous.
Yeah, it takes a few hours to load up that 64 gigs, but I don't need anything faster, at least not anything faster on read speeds. And while, theoretically, things could bog down at 20mbps+ LTE speeds, in reality most sites don't d/l at anything near that - if you get even 5mbps transfer rates d/ling files you're doing well.
For that matter, with the exception of a handful of sites pushing a lot of HD video content (like a Netflix or Youtube), most websites don't seem to load content at more than 3-5mbps.
that's pretty damn cool that they're 4x faster than the class-10 card. But it makes me wonder if the current phones are capable of transferring that fast or if it's something that we wont see any benefit from until down the line