Go for 2ms or 3ms. I game on a 5ms 1440x900 monitor because I'm poor. My eyes are pretty good and I will be the first to tell you the ghosting, albeit little, is there in fast-paced sequences. 1920x1200 is my favorite resolution, but finding a low response time monitor at that resolution for a good price would be HARD.
I've gamed on 22, 23, and 27" monitors and liked the 23" best. It was still spacious and I didn't have to turn my head a lot like I did with the 27". Anything below 22" I can't stand, even if I'm gaming on one now (too broke to replace it).