All done testing. The softmod was a success! Is it still a 100% success rate so far? BTW, I didn't download the modified bios to do it, I just used atiflash 3.09 to make a backup of the original bios, flashed an X850XT PE bios using the -newbios option (I don't remember which brand, but it probably doesn't matter), then flashed back the original bios without the -newbios option.
Max overclock (on stock cooling): 520 MHz core, 604 MHz memory
Here are my 3dmark 2005 scores with default settings. I've added in the X800GT clock speeds and the scores for my X800GT for comparison with an 8 pipeline setup at equivalent speeds, plus at some other speeds just for a comparison of what each is capable of.
Powercolor X800GT 256 MB
8 pipelines, stock clocks (472, 492): 3935
8 pipelines, max stable overclock (560, 526): 4504
8 pipelines, slightly unstable overclock (576, 555): 4750
Sapphire X800GTO2 256 MB
12 pipelines, stock clocks (398, 492): 4448
12 pipelines, X800GT clocks (472, 492): 4961
12 pipelines, max overclock (520, 600): 5563
16 pipelines, stock clocks (398, 492): 5008
16 pipelines, X800GT clocks (472, 492): 5528
16 pipelines, max overclock (520, 600): 6244
I couldn't quite reach the X850XT PE's core clock speed on stock cooling or reach as high of a core overclock as my X800GT, but it is still fast enough to get a very good score.
Until I bought this card, I thought I'd never have a card this fast so soon.