I say go for a X1950. it might be a little more, but it would be really, really worth it.
since you are going pci-e, you'd be able to get another one later and crossfire them. they have the internal attachments, not the lame external crap.
I know I'm parcial to the x1950 pro because I just got one, but if you are going ati, it's the best bang for you buck, i think.
Plus the prices are only going to come down, so you should be able to pick up a second one for alot cheaper.