I think I'm confused. If you think his card will struggle at 1440p, why are you recommending triple 1920x1080? 3x1080p is way more pixels than 1440p. Maybe I'm just not understanding your suggestion. Did you mean triple monitor 1440p? If that's the case, then yeah,
any single GPU card will stuggle
If not, a 7950 can run most games on med settings @1440p well, even at stock clocks. It's certainly not going to max out modern triple A, but you can still get good frame rates and enjoy a bit of eye-candy.
Also, while the pixel-density of a 27 in. monitor is certainly less than a 23 at a given resolution, the optimal monitor size for you depends on how far you're sitting from the monitor.
As far as cheap 27" 1080p, I like this BenQ
http://www.tigerdirect.com/applications/searchtools/item-details.asp?EdpNo=3301100&SRCCODE=WEBGOOPA&cm_mmc_o=mH4CjC7BBTkwCjCV1-CjCE&gclid=CPe48N3wibkCFchDMgod3wgASA
good luck!