While you would see a gain in performance, you must ask yourself if it's worth the money. I'm in my frugal (read: after Christmas; broke) phase right now, and I say it probably won't be. While you can get the card now, it might not be powerful enough for games that will be coming out in two years (or whenever Carmack's new game is coming out) and you'll end up having to get a new card. As it stands, you can just turn down the details in those games you play right now a bit and enjoy the extra money.
Wait until the next generation of cards comes out (shouldn't be very long now.. maybe 3-4 months) and either buy the GF3Ti200 at a cheaper price or get the newest high end card and be future-proofed for longer.
But that's my opinion. 🙂