I have two setup, one arrived dead from Scan, but they sent a courier round to collect it and now all's dandy.
I used to have a pair of WD Black's 1TB and these feel just as good to use, I've had no issues with speed or anything.
Some comparison charts :
They run only just slower than a WD drive that's billed as a fast performer (I think that's what the Black range is about..).