In that case get a 24" screen with 1920x1200 resolution. If you can stand the cost, get two of them. Also, you might want to research the differences between hardcore gaming and development PCs. Just because we run Crysis on a GTX280 and a OC'd Q6600 doesn't mean those are the best components for developing the next Guild Wars.
You should look into the merits of workstation graphics cards and the Extreme versions of processors, as well as the developer related pros and cons of Core i7's and Core2 Quads.