if its on 9800PRO chipset both 128MB and 256MB models are similar except memory type and memory clock speed:
256MB has DD2 and on 350MHz memory clock
while, 128MB is on DDR and 340MHz, still its faster.
so far only this card came on DDR2, else ATi once again used DDR in XT9800 versions.
newer models X800 sereis are coming with G-DDR3.
9800PRO regardless of manufacture, is same every where, weather its manufactured by Sapphire, MSI etc, but, capacitors used by manufacturers does as well count towards performance, and ATi of course wont manufacture their cards badly.
I have seen problems arising in Sapphire, Powercolor, Tyan etc, but never heard of any problem in ATi Built.
Intel Core2Quad 2.66Ghz 12MB L2-Cache
4096MB DDR Kingston Hyper-X
XFX 9600GT AlphaDog
Seagate 2 X 320GB SATA2
LG L246WH Flatron 24"