I am having the following setup- Athlon II X$ 620 @ 3.2 GHz XFX GTS 250 1 GB I am currently gaming at 18.5 LCD.Can I will be able to game at a 23 LCD monitor with that card while maintaining good frame rates in recent games.
The GTS 250 should handle most games at 1920 x 1080 (normal resolution of a 23" LCD). Crysis and Metro maybe medium settings.
I recommend GTS 250 for resolutions up to 1920x1080,on that res you can still play games, but you may need to turn off AA/AF in some games or lower the settings in order to get a smooth gameplay.
If you can afford an HD5770 it would be more suited for your resolution and give you DX11 compatibility.