I have both of those cards...the Ti4600 is from 2002 era and the x800xl is from around 2006 era
so I would recommend the x800 just because it supports shader 2.0 and the Ti4600 only supports shader model 1 (like the good old Radeon 8500 which it aimed to kill at the time)
The x800xl is still being used today in my Athlon 3500+ from 2006 and it's still breathing!
You may want to try to find a 6800GT if you can..simply because it was the competitor for the x800xl at the time, and supported shader model 3 before ATi implemented it on their cards.
Plus it's just simply a kick ass card in general and a great reason why everything that followed it at the time just got better, like the 7800gt, 8800gt, 9800gt, etc.