Monitors, 24 inch vs. 27 inch vs. 30 inch

I have a nice 24 inch 1920 X 1200 16:10 monitor and it is just fine. However, I will be going for a huge upgrade in the next month or two with my computer system and am considering upgrading my monitor too. Ebay has massive 2560 X 1440 27 inch "perfect pixel" monitors for an astounding 350 dollars and 30 inch 2560 X 1600 "perfect pixel" monitors for about 720 dollars.

For you lucky ones out there with these 2560 X 1600/1440 monitors.

(1)Is there much difference between the 27 inch and 30 inch monitors?
(2)Are either ones much better than my 24 inch monitor?
(3)Should I get a 27 or 30 inch monitor, will a 670 or 680 be enough?
(4)Does one need a "perfect pixel" monitor?

Just askin.