Need help from people with hardware knowledge

I am going to buy a new monitor soon but I don't know if I should get a regular monitor or a Full HD monitor.
Specs:
XFX HD7770 1GB DDR5 Dual Fan,
AMD Phenom II X4 3.4 GHz,
Corsair Vengeance 4GB DDR3 1600MHZ,
Corsair VS450w power supply,

The monitor I'm using right now is a LG 1440x900 resolution and I can play Crysis 2 at max settings (execept for vsync which is off) and I get about 40-50 frames per second.

Now my question is, will my frames drop a lot if I get a Full HD monitor?
Please help me decide.

Sorry for my english.