I have (3) BP6 systems that have all been upgraded to single CPU:
P-III/1100E/256K/1.75V/.18micron + NEO370 adapter
All three will overclock to 110MHz FSB =>1.21Ghz CPU running stable.
I advise using EverCool 715 0r 725 copper + 70mm fan cooling w/shim, available from www.nexfan.com for <$20 for all. ~90 degrees F. with fan slowed down to almost silent using Zalman speed controller.
Getting the CPU is no easy feat. Try EBay searching from the home page with either"1100MHz" or "1.1GHz" and page/scroll to the P-III listings.
pricee have been in the $100-140 range lately.
The HPT366 controller is not reliable at this speed under WinXP-Pro & I had to add a Promise ATA100 card in all (3) systems.