In My experience - A guy who changes his own oil.

I use Motul in my DC5R. 200, 000KMS on motor. Pump is on its way I think.

5w - Kept good Temps etc, but oil pressure suffered heavy.
10w - Best of both worlds, oil pressure suffers only in between 900 - 1200 RPMS

15w will be what I try next probs back to penrite. Penrite did me well when i was playing wit B series.

Idunno if this is a placebo effect. Using S2k Filter - Low RMP low pressure has increased. Only will drop around heavy corners in High g's.