Cyclocross Tire Pressure I have never raced before but there is a cycloycross race a mile from my house this weekend.   

Course has a fast bumpy downhill.  

On my mountain bike with fixed carbon fork and tubeless at 40 PSI the downhill is easy but I timed myself and I am slower by a good margin.  6:10 versus 6:30 on a three lap test course.  Even riding the CX second when I was more tired.    

A buddy of mine raced me and we switched bikes and we both agreed the CX was faster but just getting banged around too much.  At the bottom of the downhill on the CX can hardly see.  In a heat of 75 riders on a small course I want to see.

On related question someone posted a link to last year's race.  The hill I was afraid of is on the course but the decent is three long switch backs.  And even then it is late in the course so the field will be spread out.

The CX is clincher and not tubeless - that is not going to change. 
I cannot put my mtn wheels on my CX as the mtn is disc and the CX is not. 
I put the biggest tire I could on the CX (38 mm) and the lowest posted pressure for the tire of 55 PSI. 
Tire still feels hard. 
Tire does not even come close to bottoming out. 
At 45 PSI the tire starts to soften up. 

So finally a direct question.  Is it safe/sane to run a 38 mm at 45 psi when the posted range is 55-90?  I weigh 165.
Yes you can reduce the pressure and it will remain safe (cyclocross isn't a high speed high turning force type of racing). 

Your biggest issue will be pinch flats and rim protection. 

Weather and ground conditions should drive your pressure choice as well. The muddier the track the more traction you'll need.

I'd look at 30-35 psi to start and try the track on that.