Replacing the 9800 Pro for an X1600 is not really worth it
The 9800 Pro has 256 bit memory access, X1600 only has 128 bit memory
access.
I believe the 9800 has 8 pipelines, the X1600 has 12 pipelines
The X1600 has Shader Model 3.0, the 9800 Pro Shader Model 2.0
The X1600 support X.264, some sort of high definition video
Check out the X800XL, 16 pipelines and 256 Bit memory access, Shader Model
2.0
The X800XL is about 50% faster then the X1600.
I replaced my HIS X1600 Pro 256MB PCI-EX with an X800XL PCI-EX.
The X1600 cost me about $115 new, the X800XL $107 used.
My X800XL PCI-EX is one of the special ones that came with Dual DVI, the
extra power connection, Rage Theater chip
and the GPU is the R480, with is more overclockable then the R430 GPU that
normal comes with the X800XL.
I've overclocked my GPU from 400MHz to 525MHz and memory from 500MHz to
600MHz.
Added an ATI silencer 5 Rev. 2 for cooling the card.
ATI X800 PCI-EX series cards are getting cheap.
If your current CPU is an AMD socket 939
You might consider replacing your current motherboard with one from Asrock.
They have a model that comes with both AGP & PCI-EX and still use DDR
memory.
It would allow you to get the PCI-EX cards which are cheaper then AGP.
Sell off your 9800 PRO