Intel overdrive DX4-100 has passive heatsink glued on at the factory
AMD 586-120@160MHz (aka PR75) I use active (you could try a BGA cooler).
i486-DX50 (not dx2-50) I have with passive heatsink glued on by integrator.
I had i486DX/33 without heatsink, one i486DX/50 was at work (no heastink too). Then I had STMicroelectronics (Cyrix OEM) 486DX2/80 with heatsink and fan - however the fan died so I removed it and it still works fine I have also one i486DX2/66 overclocked to 80 - it requires heatsink AND fan to be stable.
Have, or had really, an IBM ps/2 with an Intel 486 DX2 50MHz (stuck on socket on cpu board).
It has no heatsink but the case was well ventilated.
I only have the cpu board left now the machine is going to the dump tomorrow.
disabling turbo mode would put it into 33mhz enhanced.
I do it when I donthave aheatsink but i wouldnt try it ona dx-100 lol.
thus 33 enhanced is safe withoutheatsink in myexperience but i dont remember my dx-50's core voltage.
Such huge landfill new tech costs when all we need is scaleability.