Dell U2412M 24" will give you a 1200p resolution which IMO looks better then 1080p.
Review. It's missing modern day features like a USB 3 hub and unlike previous models it doesn't feature a card reader or have HDMI out (which isn't all that relevant as you want to run this at 1200p which HDMI can't support) so I would suggest running this of the display port.
Of course you could save up your pennies and go for the Macdaddy of 24" screens Dell U2413 which has a full 8 bit display, card reader returns, D-sub is dropped and HDMI makes a return in terms of output and best of all at the moment this is under your £450 budget.
Just to prove I'm not a total Dell fanboy you might want to consider the
DGM IPS-2701WPH 27", again under budget, IPS (i.e not crappy TN display with washed out colours), display port, DVI, D-SUb (VGA) and HDMI (although you don't want to use HDMI). The best thing about this screen is frankly it's cheap for what it offers and gives you a max resolution of 2560 x 1440. Of course there's some cost cutting, 6 bit display (same as the Dell U2412), cheap stand/only tilt adjustable, no card reader, no USB hub. It's worth considering but you will be wanting to upgrade your video card more often if you want to drive games at it's native resolution but a 7950 will cut for now.
I have Dell U2407 which I have had for years and years now, it cost an arm and leg to buy back in 2007 but it's proven to be fantastic value for money as I have no need or desire to replace it with a newer model which only offer incremental improvements. Competitive FPS games on IPS displays can show up their short comings, I used to play CD4 a lot when it came out and was pretty good but every now and then I would get killed by even though I thought I had shot the guy first, this was the only time I noticed the input lag on this display. I wish I could blame my battlefield 4 performance on input lag but in reality I just suck at shooting straight, all other online games are fine though and keeping with IPS you will appreciate the better colour depth and vibrancy on display.
