Like oldfart I'm kinda partial WR to the upcoming 0.13 micron "Tualarons". The 1.0A @ 1.5 sure looks promising, especially since the prices for the 1.0A and 1.1A are supposed to be the same as for the current 0.18 parts. I think I'll build a new box for me when they are finally out.
That said, I'm still using dual PII 450s on a Gigabyte 6BXD. A very nice combo in my experience, and I'm certainly not getting rid of it once my Tualaron is here. Battle tank is the best description really: slow on a straight line, but it turns on the spot

- and the stabilty is legendary.
To help you decide for or against the BP6 (or SMP in general):
IMO the BP6 is not good with 500 or 400 PPGA celeries. You'll be locked at 66 or 75 MHz FSB with them, which really hurts performance. The 400 might take a 100 MHz FSB with drastic cooling measures and a lucky selection of late week chips, but your current setup would still be far more stable. Running 83 MHz FSB might get you in all kinds of troubles because of the highly overclocked PCI bus.
Best choice of CPUs for the BP6 would be socket 370 PPGA celerons 300A, 333 or 366 that can handle a 100 MHz FSB and clock at 450, 500, 550 MHz respectivly.
So let's say that you can find a real cheap combo of a BP6 and two 333s running at 500. Would you enjoy that more than your current Duron?
Stability would be BX typical as long as you don't use the onboard RAID controller (it plain sucks and is best left totally disabled), so that's a big plus.
Compared to your duron, raw speed would be similar at best in SMP aware apps, and much much slower in anything single threaded. Especially for 3D gaming the BP6 would be a massive step backwards (even with the handfull of SMP aware games).
But there's one biiig advantage of SMP that, depending on what you do with your computer, might be worth those downsides (and that's the reason I'll keep my dual box): your BP6 will be more like two celeron 500 machines in the same box, controlled by one keyboard and one screen, than a 1000 MHz machine.