The premier class (500cc 2-stroke or 1000cc 4-stroke) Moto GP bikes were all 2-strokes a few years ago. Recently, due to changes in regulations, 4-strokes have taken over. The 125 and 250 classes are still 2-strokes. BTW, in all 2-stroke classes the individual cylinder displacement was 125cc (i.e. the 250's were twin cylinders, the 500's were 4-cylinders, the 125's single cylinders).
I don't know what type of premix they used, but it would probably not work well for a dirt bike. These bikes are very highly tuned - ~190+hp for the 500cc bikes, and are run very hard and re-built after each race.
I'v run Yamalube 2R in my KDX200, KX250 and KX100's since the 1997. The top ends seem to last very well and stay extreemly clean.