Stepping SL36A of the good old Celeron 300A.

I got one completely stable at 2.1V at 600 Mhz on an Abit BH6, rev 2 board back in 2000. I felt like I'd won the lottery. That was probably my favorite moment in computing history. I had finally achieved the holy-grail: a 100% overclock! Twice nomimal CPU speed! The system screamed at the time. Paired with a V3-3000 AGP and 768M of RAM.

I proudly still own that system to this very day.

The Tualatin-S and close second is the 486DX4.

Both are very powerful CPUs that can cover most of the 90s on their own and their compute power overlaps at just the right place so used in combination they can cover even the speed sensitive stuff from the mid 80s up to the resource intensive stuff in the early XP era. I place the Tualatin first, because I'm more interested in the mid-90s and early-2000s era.

Maybe the third would be the K6-II+ which can sort of do the same in one product, but lacks at the extreme ends of the time frame.

Via C3 Ezra 1ghz. Flexible, can run passive, lots of nice ATX mobos, perfect for dos to 1998. Looks cool. Something different to AMD/Intel.