I am just wondering if Mobile 1 extended performance is okay to use in a 2.3 Miller Cycle.

 

it is fine, but overkill. ext service is designed for cars like bmw, that have 15k service intervals. if you really want to know, put regular synthetic in, then after a few thousand miles, get an oil analysis. do it again after several thousand more, it will tell you when you need to change it. bmw oil is castrol, and most of the independents have stopped using it because of the extreme foaming, which causes premature breakdown. most have switched to mobil 1