Once again Folks there is a lot more to pressure than Max Chamber Pressure only. Obviously when you reduce the chamber to that of a 12ga chamber pressure would not be expected to change much. As it passes from the adapter into the bore itself pressure will drop below that of a 12ga bore.
Personally i would "NEVER" use 7625 at pressures of 5k psi, certainly not if temps might be expected to drop enough for a long sleeve cotton shirt to feel comfortable.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra