I would be more concerned as if it would fit in your case.
if it does, then go for it.
Also like others said, DD3 (RAM) and GDDR5 (MEMORY RAM) have nothing to do with each other.
Ram runs your OS, Programs, games...
GDDR5 runs your VIDEO / GAMES (specifically designed for video intensive applications and games)
a lot faster than say a GDDR3 video card.