Maybe I'm uncool, but what business does a hardtail have with a 150mm travel fork? I should think anything that needs 150mm of travel would have rear suspension as well.
Your air pressure should be set such that you bottom out once per ride. That is a spring rate question, not a suspension travel question. A hardtail isn't/shouldn't be doing Downhill or mega-jumps or trials in rock gardens. A hardtail is for trail/singletrack/cross-country. Setting a 150mm travel fork so that it has so much cush that it bottoms out onces per ride on cross-country would have silly sag & über squish. In addition to converting your bike to ride like a boat, it'd have all the feedback & response of riding a sponge.
I really think you'd be better served by something similar to factory specs & run the air pressure a bit on the higher side if you find yourself bottoming out.
Last edited by base2; 01-28-21 at 09:21 PM.