Right now if given the choice between the GF4 Ti or GF FX I would go for the GF4 Ti and save my money for a more proven newer FX release - released after even the 5900.
I don't want to turn this into a NVIDIA vs ATI debate but The Radeon 9xxx line has already proven itself in the real world whereas I still have yet to see enough from the NVIDIA FX line. I was a 3dfx lover until they died and I was forced to switch over to NVIDIA and I got a GF3 which I love. Well, the time will come to move on to a more powerful card. For me, right now, that next card will NOT be an NVIDIA card. I am not at all impressed with what I have been seeing. ATI, a company I always disliked... has shown me a lot recently. My next card will likely be an ATI AIW 9700 or newer card.
So, for now with the current games that are out I think the GF4 Ti should be enough and you can then save up your money for when you really need a DX9 card that can kick butt.
Just my two cents.