Setting aside the servers at school (which are multi-user UNIX machines...and would be difficult to compare performance against...as I never get use to the systems full resources), I would have to say either:
DEC Alpha 600 MHz, (forgot how much RAM), and winNT 4.0
Was down at a comp shop, where I had one built (prior to them going outa business). Needless to say, we had become acquantances, and latter friends of sorts. One day, when they built this system for one of their customers (to become a server), Fred told me to take a look in the other room. He had something to show me. It was this system. Wasn't much software on there, but I did get to use a bit.
- else it'd be split between my AXP 1900+, 512 MB RAM, 10k RPM ultra160 SCSI drive (for the main one, the other a 10k rpm u2w SCSI)
else a P4 2.5 GHz, though the RAM might be less, the gfx card not as good, and the drives slower. Guess it depends at which components you're looking at.
So why do I mention these, if I had used an Alpha? Because the Alpha was among the fastest kids on the block when it was new. However this was 5 or 6 years ago. Even with the PCs being slower within a given generation, things do in the fullness of time have a way to catch up. As I remember, it was also an Alpha 21164 (not the 264 that came out, before Compaq which acquired it, then killed the platform going with Itanium).