no, the amount of RAM has no bearing on how powerful the GPU is.
if its ATI anything with a number higher than HD5670 should be good.
with nvidia, anything higher than GT330
but the amount of ram is not a figure to look at.
EDIT: now that im looking at the specs of the first one you linked, and done some more searching, it seems it may actually be a GT335m. in which case its performance is about on par with the other 5670. but given the price difference i'd go for the second anyway.