Hi Chris,
I believe you currently have a 2407 correct?
I used to have one of those, tried a U2410 for a while (2407 was better), then went through a range of 24" including 3D ones and then started on my mission through a few 27"
Recommend without a doubt to go 27" 2560x1440 (dont even look at the 1080p ones).
Think your choices are basically Catleap Variants, Hazro Variants or the Dell U2711. Picture quality wise the Catleap is the better, but for build quality, warranty, peace of mind etc etc the Dell can't be bettered.
Unfortunately it's darn expensive. If it was my money, i'd get a pixel perfect catleap (which I did actually) which will set you back around £215 all in, including any import taxes. You could sell your 2407 for what? £150? Not going to break the bank then.
Catleap is a significant upgrade over what you have now. Once you see 2560x1440 in action you will never go back to 1080p