My DDR based QDI Advance 12T is easily the fastest P3 board I've ever tested, beating out BX, i815 and i820 in all benchmarks I've thrown at it. That's with some pretty speedy 2-2-2-5 DDR running at 155MHz (310MHz DDR). Like I said before, it can handle 720p H.264 in software without dropping any frames. Even "tricky" video with lots of fine detail works just fine.
WMV-HD at 1080p is also doable with a Radeon 9800 Pro performing partial (shader-based) WMV acceleration. Interestingly enough, my GeForce 6800GT doesn't seem to do any WMV-HD acceleration at all. With that card, 1080p WMV drops a ton of frames. Still, at 1.63GHz, the PIII-S is plenty fast to handle 720p WMV in software.
I do wonder if a dual PIII-S @ 1.63 would be able to pull off 1080p H.264 decoding in software. The dual 1.25GHz G4s in my Powermac MDD can actually handle 1080p (barely), so dual PIIIs might have a fighting chance.
94 MHz NEC VR4300 | SGI Reality CoPro | 8MB RDRAM | Each game gets its own SSD - nooice!