The .30-06 is a wonder cartridge despite the fact that some consider it boring. It will work really well with a number of different bullets and powders. It is not surprising at all that you are having great results with IMR 3031 powder and the 150 grain bullet.

I've found that IMR 3031 works about as well as IMR 4064 or IMR 4895 with both 125 grain and 150 grain bullets in several different .30-06 rifles kept around here. One can duplicate 150 grain factory velocities using 3031. A powder like IMR 4759 or IMR 4198 would be way too fast. IMR 3031 isn't too fast.