$200+ for the GF2 PRO, and $400 for the GF3. Wow, that's a tough one. Those prices are right on the borderline of what my decision would be. I mean, if the PRO were a little more, or the GF3 a little less... then I'd say to go with the GF3.
But if you made me decide right now, I'd still say to go with the GF3. For a few reasons:
1) You won't regret the GF3. There won't be any "what if?" in the back of your mind. You might end up kicking yourself in the near future, for not going for the GF3.
2)Some say to get the GF2 and wait until the GF3 comes down in price, and sell the GF2 at that time. Well, the GF2 won't be worth much at that time. So, are you really coming out ahead in the long run?
3)There are features in the GF3 that today's games can take advantage of. Speed, especially at high resolution. Quincunx FSAA (which is much better than the GF2's FSAA). Better 2D quality, if you happen to get a GF2 with poor 2D quality.
Hope this helps. 🙂