FWIW most max loads in Nosler#5 are in the neighborhood of 3350 with a max load of AA8700 reaching just over 3400. However Nosler doesnt show data for Hodgdon H-1000, Retumbo, or RL-25 which should all work well in this gun.
I would expect a max velocty for a 140gr Nosler to be in the neighborhood of 3450 with the right powder in your STWAI.
I would start with AA8700. It works great in my 7MM ultra.
