Before I retired it I ran an AMD K2. It has been a while since I last looked at the stats for it, but I think it ran some jobs, I think they were FAAH) in excess of 60 hours. When the stats finish updating I will take a look and see if I can figure out how long they took. Even I had to admit that the machine was taking more electricity than it was worth, so I retired it and gave it to one of my brothers who just uses it for some word processing, spreadsheets and email. Not that I would want to try it, but I suppose one could find an old Pentium 60, load BOINC and see how long it took to do a couple of FAAH units or HPF2 units. This would have to be just to satisfy the academic curiosity as it would definitely not be efficient. Perhaps some one smarter than I could extrapolate how long an average workunit of one of those might take without actually having to find one to fire up. I think a 486 would not meet the requirements, but it would probably be quite a bit slower still if it did.

(edit) I just looked up the CPU rankings on BOINCSTATS. According to those, the newest Q95xx series is about 83 times faster than what is listed for a Pentium 75-200. That is the lowest listed cpu.

Cheers