SLI 450's are actually about the same speed as the GTX470, which is in turn around the same speed as a GTX560ti. I've not seen benchies of the non-Ti version, but it seems likely to me that you'd end up w/a small decrease in perf (speaking of avg fps) if you switched to it.
However, at lower FPS, single GPU solutions usually feel 'smoother' due to the microstutter effect that is common at low FPS with multi-GPU setups. To use numbers to illustrate, a game at 30fps on a single GPU is usually pretty playable, but a SLI setup running at 30fps will often 'feel' pretty laggy.
Because of this effect, it seems probable to me that your max playable settings either wouldn't change, or may possibly go up slightly if you were to do this switch.
Also, Tada, we have a 24-hour rule when it comes to thread bumping on OCN (the bump post has been deleted).
Edited by brettjv - 5/25/11 at 12:13pm