If you look at a Load/Pressure Chart, being sure to take Single vs. Dual into account, you'll see that 60PSI Single (Front) equates to the GAWR of the 4600# front axle E450 used through 2007 (chassis year) and that 65PSI works out to GAWR of the 5000# axle used from 2008 up.
What this information adds up to is that over 65PSI is not needed for E-Series Front Tires.
Doug, FYI, turned out our E450 is at 4500 front and 8800 rear. You asked and I never sent the info. So here it is, with apology. Using Micheln's chart, that works out to about 60 front and 75 rear.