no it will not depend on the RAM, bit rate or the GDDRx (It may though, but only when you are comparing the same model)
This is a good table showing performance in general:
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html
I will show you why it is not depending on RAM or bit-rate
GTX 680 has 2GB RAM and 256 bit, and HD 7970 has 3GB and 384 bit. The 680 is about 10%-20% faster in gaming. A GT 440 which has GDDR5 gets beat out by the HD 6750 DDR3