I couldn't tell a bit of difference between the two (162gr) ballistically speaking. I have shot both bullets with the exact same load out to 700-800yds and there was virtually no POI change, same dial up. Further may show more of a difference but I didn't see any at the ranges I shot at. My particular rifle did like to be close to the lands. I tried .020 and .025 off and it was a no go with huge groups. .012 and closer they shoot great. Not sure how they will do in yours though, just gotta try it.
Bullet RPM is just math. Plugged your RPMs into the equation, solved for x.
It's RPM = MV*720/twist rate.
Experience in rifles doesn't mean they can do 4th grade math, or you misquoted them. Probably the latter, as almost nothing spins at 400k rpm. The MV and twist rate required to do that are not common.