Some newer games will choke on my 6800GT at 1680x1050 if I have 4xAA on, and often (unless I'm limited by shader performance like I seem to be in HL2) reducing it to 2x will help a lot - turning it off completely is often not much faster, if at all. I can definitely notice AA at this resolution though; ideally I still want 4x if I can get it.
There aren't really any other (lower) standard 16:10 resolutions (although I added 840x525 as a custom mode, due to the supposed 1-to-4 perfect pixel scaling - but that's just too low). I tend to avoid resolution scaling anyway unless I don't have a choice (i.e. the game would be a slideshow at native res - which luckily isn't the case for anything yet...)