At that resolution AMD'd Fusion APU's game spectacularly well . They're true quad cores manufactured at 32 nanometer and are often the best call fora machine like yours . The graphics built in to the processor is really capable , and if you add some AMD graphics cards it crossfires the two graphics systems
I havent priced them but
AMD A8 3850
FM1 motherboard with an A75 chipset
1600 Mhz or 1866 MHz RAM running at 1.5 volt
the A8 will play any modern game at medium settings at 1680x1050, for 1024x768, it'll do them at high.
there isn't much downside at your screen resolution. Its not as powerful as a Sandybridge, but its plenty adequate for most use -- that's why it's the sweet spot for htpc/basic computer systems, and can handle low end gaming