The only difference between them is clocking (the sapphire has 100Mhz more on core and more on memory, too). They are pretty much cheap so the cooler is almost the same, I guess. The warranty is also the same (lets say the services are too).
So the final question is: which one looks like it has better cooling?
as jtenorj said the 7750 is too slow to utilize 2 gigs of video ram, its a marketing practice as I have seen numerous low end video cards with extra ram that won't really benefit them but you will be charged with extra ram
I totally agree that 2 gigs are in vain too much for such a card.
I think I´ll go for Sapphire then, since it's "oc'ed" already (I don't really want to OC on my own)...but any of you guys can post here if you got any problems with that SappHD7770.