er... which cards are you talking about? i've never heard of a 5760. oem card?
difference between 5670's ddr3 and gddr5 (not ddr5) version is that the gddr5 version is faster in performance, uses a little bit more power.
if you're talking about a radeon hd 5750 ddr3 - the gddr5 version is better because of much higher memory bandwidth.
prices vary at different locations. in some places the difference is minimal while in others, bigger.