Help picking the right size monitor

Background: Ive had a samsung syncmaster 730B (1240x1080) since december of 2005. was used with a readon x700.

Now ive just recently built a new gaming rig, and considering the MASSIVE upgrade, im not seeing much of an improvment in games. Im 90% sure tis because of the size of my monitor, being as small as it is. At this point ive saved up about $350, and will have close to $450 by next week. I want to get a new monitor to really use my computer for what its meant for, at the resolution it can play at.

however i am at a crossroads. a 22" 1680x1050 is anywheresf rom 250-350 in proce, but a 1900x1200 is around 400. what would be the best bang for buck for my system, and furthur systems down the road?

Specs:

DFI DK X38
Intell E8400 oc`ed to 3.4
4GB ddr2 800
HD4870

Thanks guys,

What i ment was, this new computer is such a leap from my old computer, that i was expecting to see more of an improvement then i am. and i think its due to this current resolution being controled more by the cpu then the graphics card. so, to use more of my graphics card, what resolution would be better, without hitting big performance hits.
i am aware that higher resolution means lower performance, but im getting around 70 in cod4, with my x700, i was getting 50`s