Off road tri - mtn bike tire pressure

depends on the course, the bike,  rider weight, tire size, and a few other things

Generally, for me at 200+ pounds, on a Fuel, running 2.3 Continential vertical Pro's on a mixed (some rocks, some clay) course I'll run 40-42 lbs

65 pounds is way too much for anything but asphalt

dirt is different that asphault. With the road you want as little of your tire as possible touching the ground to reduce rolling resistance, hence higher pressure.  On dirt you want plenty of contact so you can grip the dirt and you don't spin out.   I'd say 30-40 would be a good balance.    If it is hardpack, you can go a little higher,  Gravel, or sand, go a little lower for more grip.  

I tend to like them a bit harder.  I read the article referenced but my limited experience has me lean toward a bit harder pressure.  I run about 45 for a dry, hard track.  I do skid a bit there but for me that's ok.

I'm jealous, I got into this sport thinking I would be doing those races but they quit doing them in MN after my first one.