depends on the gpu and the make.... like i know many of the last gen nvidia cards.. such as the 5500 and 5700, the 128MB versions were much more reliable and faster for gaming than the 256 MB versions as they had to change the architecture in many of the cards to support the extra ram and that caused a decrease in performance... like i said it all depends on the make and model
EDIT: blast u beedub lol cudnt wait 2 more seconds until i posted haha