Good question, and usually that is reached right after starting a cold engine in cold temps. I did blow up an oil filter once on start up in 15 degree temps using 20w-50 Redline in a freshly rebuilt 2.1.  Didn't have a chance to see the guage at that instant, but it was a 0-80 psi gauge and it must have pegged anyway. 

The point of a guage is to track trends and pressure under various operating conditions--notably decreases with high temperatures and extended running.  Gauges are only useful if you check them frequently, and then you can ignore them (like I did with my used 2.1 13 years ago: http://volksweb.relitech.com/21rodbrg.htm ) but at least be aware there is a problem!

This story demonstrates Dennis' point on oil pressure and WBX main bearings.

Stuart
Older, and maybe wiser

. . . .So, what is "too much" oil pressure in a waterboxer?  Mcneely