From what I understand, your graphics card has either one DVI connector and one VGA connector or both DVI connectors. I assume that you have your current monitor plugged into the VGA?
I have recently changed monitors from a Dell 19" FlatScreen monitor that was just VGA to a Samsung SyncMaster 950MG LCD TV which is suited for both PC and TV use. As it is a new monitor, it of course boasts a higher contrast ratio, DVI + HDMI + Component support and a high brightness level.
If you were looking for a nicer, sharper and overall vibrant picture - I would recommend getting a Digital LCD (preferably HD ready if your looking for a LCD/TV combination). DVI gives a pure digital and quality picture, here is a quote from CNET:
When connected via an analog connection, an LCD is vulnerable to the same distortions that affect CRT monitors. However, when connected via a digital connection, often labeled DVI (for Digital Visual Interface), no digital-to-analog conversion is required, and there should be no loss or corruption of the signal. As a result, when running at its native resolution, an LCD should give you a cleaner and crisper image than you'd see on a CRT.
Also, you mentioned if the performance level would go down. It would drop if you were at higher resolutions but from you PC spec, it looks ok.