I am really conservative when it comes to hths and turning 6000 rpm's or more regularly. Heat, Pressure, Shearing and turbulence can get insane as rpms increase a lot at the main bearings. Heat and friction at the wrist pin is crazy! Think about how much sliding is going on between a ring and it's bore at 9000RPM???? The hths, long term shear stability of VI's,and additive package between the various XW30 oils is all over the place. As sustained RPM increase this sort of stuff matters.