I agree with mapex. For that resolution & with the 4600, the GTS is even overkill except for Oblivion.
Check out tom's review of the 8800 series with the fastest desktop chip available, the X6800. It's rather enlightening. Here.
I'd wait for DAMMIT to get into the playing field and get a mainstream DX10 card. But if you just have to have it now, the GTS will be more than enough.
Btw, what's your PSU specs. You're probably fine but it doesn't hurt to supply them to be on the safe side.
Larger monitor would make a huge difference, if it's huge enough. Higher Native Res = More GPU Power Required. If your getting something 1920x1200 or higher, you could benifit from a better graphics card, otherwise it's overkill. Stick with what you've got. (BTW, you have too much money if your planning to upgrade your monitor and graphics. I am accepting charitable donations.)
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