Please remember that any mention of competitors, hinting at competitors or offering to provide details of competitors will result in an account suspension. The full rules can be found under the 'Terms and Rules' link in the bottom right corner of your screen. Just don't mention competitors in any way, shape or form and you'll be OK.
If it's single screen you might be better off just sticking with the 670's as they'll perform identically to anything else (i.e. bloody smooth!)
If it's multi screen/high res I would persist with the AMD option due to how much quicker they are in this scenario.