3e/PF to 5e Conversion

I ran a bunch of Pathfinder adventures using 5e. It is definitely harder than running OSR material in 5e, but remains doable. I had several handy monster conversion metrics:

Halve AC over 10. Halve stats over 20 (& cap at 30, obviously). Increase damage +50%. Increase hit points +50% at levels 1-10; at very high level the listed hp are often fine as-is. Ignore feats and weird crap on multi-page stat blocks, but look out for signature abiliities to convert.
Finally, calculate attack bonus & save DCs using the 5e rule of Proficiency + Stat bonus, +8 if it's a save DC.

This works great 95% of the time. I occasionally fluffed when eg converting to Legendary status, the headless horseman who could throw a 15d6 hellfire ball 4 times/round was a mistake - with massive damage spell-type attacks you may want to keep the 3e/PF damage as listed.