He's got a single 7970 so I'd go with the 24" 1920x1200 dell. I know when i had my 7970 on my 27" 60Hz 1920x1080 asus monitor it sat at around 60fps on BF3 full maxed. wow you wont get much more than 60 fps and shouldnt matter vsync that so u dont get screen tearing.
also 1080P looks like crap past 25" trust me my next monitor will be a 2560x1600 30" sometimes i feel like my 1080p is 720p cause the screen size.
---------- Post added 2012-05-29 at 11:56 AM ----------
I played the crap outa unreal tournament back in the day when i was on campus.