Tire pressure is going to be variable (at least for me) on the trail, bike, my weight, my risk adversion (how much I am worried about burping the tire or bashing a rim).

For example Sunday I rode at an extremely rocky trail, I wanted a plusher ride so I set my tires at 26 back, 25 front. I am running full suspension, weight about 160, however everyone that watches me ride says I ride light. What do they mean? I am not a super aggressive rider, I tend to take the "hardtail" line and definitely do not huck anything. Whatever it is about my riding style I get about double life out of chains, cassettes and tires if just wear and tear is considered. Other thing to consider is your rims, my husband rides his 29er at 28-29 because he has carbon rims and doesn't want to take the risk. Plus he is "big" by bike manufacturer standards for light parts he is 6'2", 180-185. Cracks me up, he actually is too heavy for my wheelset which is only rated to 175. He looks pretty darn lean to non-cyclists.

On a hard packed trail where I don't need as much plushness I will run mine closer to 28-29 depending on how much I need to corner fast. If it is really loose (like Texas is right now), I may drop it down to 27 but still a little firmer.

Of course I am still in the experiment stage because my 29er is the first bike I could feel the difference on. It is also the first bike I have had with a good, super stiff wheelset that is making me notice the wheels/tires more.