you're in luck.
I'm running a T-bird 1.1, with a EVGA GTS 32MB, and I recently hd the oppurtunity to try out two vid cards in it.
A PNY ti4200 64MB
and a Radeon 9000 Pro 128.
You should be getting 3dmark scores a tad under 4000. I was getting ~3600
The R9000 Pro gave me an increase to 6800
The GF4 4200 gave me an increase to 7200
Honestly, the picture quality of the Radeon is better, IMHO.
Im running the PNY now, but will probably return it also. Been holding out for a R9500 Pro, but it doesn't look like its gonna happen.
My advice would be to go and pick up one of those BFG4200's @ BB and then get a price match on Black Friday. 89 bucks can't be beat

.
P.S. I'm running this PNY @ 4400 Speeds, and thats the 7200 number. Highest this card will go. @ 4200 speeds its between 7000~7100.