Also, a midrange option could be a Ti4400---if it's not that much more than a Ti4200.
Also, consider what gaming your gonna do, how much, and what resolution you'll be doing it at. I've got a GeForce 3 that still runs everything smoothly, except the UT2003 demo at 1280x1024 in 32-bit color just fine. With some tweaking, that can achieve smoothness. The Ti4200 is a safe bet, but you may want to consider an ATi Radeon 9500 Pro card, as these are about the cost of some Ti4200's, but can compete with the Ti4600's.
These are all good options, but just don't plunk down a wad of cash for a card just to have the fastest one if you're gonna spend more for a card that just gives you a higher benchmark score.
In all honesty, I can still get by just fine in most games with a GeForce 2 Ti and play at an acceptable resolution to me with a number of enemies on screen. That's why I'm saying you don't have to spend the big dough for the Ti4600. You can probably OC it to Ti4600 speeds pretty easily, like Syngod said, if you want a speed boost later on and if you feel like it.
There's always gonna be something bigger and better around the corner, and the prices will drop, but you may have to wait a bit for the GeForce FX to come out. ATi has the successor to the Radeon 9700Pro in the works as well, just so you know. It's a never ending cycle.
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