the quad will be fine, the GPU will suffer horribly even at low you'll struggle unless you drop the resolution. Either buy it before the new card (so you get that lovely feeling of wow its worth it), or there are/were some cards that came with it.
560ti will be fine at 1080p at medium/high, but not ultra, 1GB of vram may not be enough. Hope that the 660ti has more memory. Though the 570's are now a lot cheaper.