X-bit Labs has compared the ATI RADEON 9000 with the RADEON 9000 PRO and some other 3D cards :
Well, the old buddies NVIDIA GeForce3 Ti200 and ATI RADEON 8500 LE 128MB are still pretty strong and don't want to give up their positions.
ATI RADEON 9000 PRO based graphics cards were slower than ATI RADEON 8500 LE 128MB in nearly all benchmarks and showed about the same results as NVIDIA GeForce3 Ti200 or a bit higher.
The slower ATI RADEON 9000 based cards were about 15-20% slower on average than those on ATI RADEON 9000 PRO and a little slower than NVIDIA GeForce3 Ti200. The reasons are evident: lower graphics memory working frequencies (400MHz (200MHz DDR) against 550MHz (275MHz DDR) by ATI RADEON 9000 PRO, which is 27.2% lower). The lower chip frequency (250MHz against 275MHz, that is 9.1% difference) affected the results less drastically.
As a result, ATI RADEON 9000 would perform 9.1%-27.1% slower than ATI RADEON 9000 PRO depending upon the specific application. Of course, the loss would be less evident in systems with slow CPUs or when the graphics card performance is not crucial.
The advantage of 128MB of graphics memory over 64MB is hardly noticeable in most tests. I would prefer the 128MB variant of an ATI RADEON 9000 / 9000 PRO based card only if it cost just a little more than the 64MB one.