I run at 1680x1050 16xAF and 4xFSAA, it struggle a bit with full fields on a couple tracks but otherwise it looks superb.
Up to a point resolution doesn't seem to effect frame rates all that much, don't run LFS at the lowest res assuming that it will get you the best fps. I mean it probably does but the next res up might only cost a few fps and look a whole lot better.
Also anything above 60fps is pointless imo, I'd be increasing picture quality through resolution, AF and FSAA till you can get something steady around the 60fps mark (I run a steady 50fps).