Didn't even knew there was a DDR3 version.
GDDR5 and DDR3 are types of memory used inside the video cards. They do not require different slots or different power supplies. The slot and power requirements are inheritant to the model of the video card, not to the type of memory used.
Anyway GDDR5 is way waster than DDR3. It can transfer information faster from the memory to the GPU and back. But to transfer that information there is also a connection between them, called a "memory interface". That memory interface has width measured in "bit". For example GDDR5 at 128 bit will be faster than DDR3 at 194 bit. But DDR3 at 194 will be faster than GDDR5 at 64 bit.