To answer the OP's question, I don't think there's enough "+P" there in an '06 case to justify creating a class of ammo for it.
The .257 Roberts is widely available in a +P designation, but there is a significant difference in pressure limits between the two, so for people with modern rifles it's worthwhile to have the +P loads. That's not really true in the '06, when you're talking about going from 60ksi to 65 ksi. And if someone is silly enough to stick a 65ksi load in a Garand, or one of the common '06 pump or autoloaders, it could damage the gun.
I've got a few guns that I run above book loads, but in those cases I've studied the data very carefully and have worked up loads watching chrono and case expansion data, but I don't claim anyone could use it in their rifle.
