As Bond007 also said the thing is that the 3gigs will help you only if you are running extremely high resolution and multiple monitors. Assuming you are running 1080p (most are) the 670 will by far be the faster card. So I'd put my money there definitely.
Hardware Canucks is focused in-depth reviews of the the latest graphics cards, CPUs, storage, smartphones, notebooks and gaming peripherals. Join us as we unbox, review and benchmark the best computer hardware on the market.