i play BF3 on 27" 2560x1440 and 24" 1920x1200. I actually prefer the 24". you can read the blogs of various fps pro gamers, most of them do not like overly large screens. I'm using 7950 2560x1440 BF3 on all high settings, minimum 40fps. average 50+fps.
For RTS, bigger the screen the better, but note that 27" 16:9 is not that much bigger than 24" 16:10.
For RTS, bigger the screen the better, but note that 27" 16:9 is not that much bigger than 24" 16:10.

