1680x1050 - Max Quality
When running Borderlands 2 at 1680x1050, we found what looked like a rather severe CPU bottleneck -- a surprise given that we're using the Core i7-3960X. The frame rate would spike to around 120fps with the higher-end cards, however, out on the ice ledge where the majority of the test took place, the frame rate was limited to 75fps.
As a result, the top 10 graphics cards starting with the GTX 480 were limited to an average of 75fps. The older HD 6970 managed 73fps, a frame rate the GTX 560 Ti also managed to achieve, despite usually being slower than the HD 6970. Similarly, the GTX 460 kept pace with the HD 6870 and 6850. Again, this is a "TWIMTBP " title.
What we can take away from these results is that at 1680x1050, only very modest GPU power is required as all graphics cards averaged more than 35fps, while most of the affordable cards managed a decently playable 50fps or so.