I found someone selling their GTX 580 (of that model) at a low enough price that after selling my card, the upgrade would cost me about $30-$40. But my 560 Ti can already run everything I throw at it at full settings and close to 60fps, except Metro 2033 and I am assuming that's at least partly because it was poorly optimized when ported to PC's(?). I'd just like to get a better idea of how much of a difference there is in the two cards before I commit to buying it.
If it helps, here are the other parts in my computer: Processor: Intel Core i5-2500K Sandy Bridge 3.3GHz Ram: Kingston HyperX Blu 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 Motherboard: MSI P67A-G45 (B3) LGA 1155 Intel P67 SATA 6Gb/s USB 3.0 ATX PSU: CORSAIR Enthusiast Series TX650 V2 650W
The relative performance difference is about 29% at all resolutions:
If you planning on playing at 1920x1080 it would be 34% difference: