The 580 is indeed faster though not by a huge margin and you get DirectX11 support which the 295 doesn't have. However, depending on your screen resolution, outside of DirectX11 support you may see little benefit in upgrading. If you aren't using a monitor above 1900x1200 or gaming across multiple 1080p monitors the performance gains are not likely to be noticeable under most circumstances. Only really demanding titles like Crysis 2 or Metro 2033 would likely see any significant performance boost on a single monitor setup.