10W60? I'm with others here, that's WAY too high, even with your previously stated 4.5 bar at idle and 6 bar at speed. Keep in mind thinner
oil actually lubricates better, as flows better (particularly when cold) and is better able to work it's way through tight clearances.
I'd try 5W40, probably even 5W30. As long as you're maintaining 10 PSI/1,000 RPM (0.7 bar/1,000 RPM) your engine will be fine. IOW, at 5,000 RPM 3.5 bar (50 PSI) is sufficient for a long and healthy life.