I have a GF4 Ti4400 and I'm jonesing for this card, big-time. I would agree with your statement if you qualified it by saying that if you don't use AA and/or AF you don't need to upgrade. I don't know about you, but on my P4 2.4B rig, AA and AF bring my GF4 to its knees.
In my experience, enabling Quincunx AA with AF pretty much cuts my system performance in half. But once you get used to playing games with those features enabled you can't go back. The GF4 Ti is just too slow!!! Even with AA and AF off it still can't keep up with my CPU.