I'd try 42-44 but it really depends on what brand of brass and head space setting. The reason I say that is because I set up my barrels on new brass so there is zero head space,, I use Lapua brass which is rather thick and a fairly tight chamber, I don't have to run as much powder to get the higher velocities. I have been running around 41.5 IMR 4064 with a 168 SMK, and 41.4 IMR 4064 with a jammed 178 Amax nets 2700 fps from 26" barrel.