Good comments by all, thanks.
I plan to stick with the 0W-40 and am showing great results. 3ppm increase in iron is really not significant. We run Mobil 1 in our cars and the iron results are at or below the universal averages.
0W-40 is a good compromise for me, thicker than 10W-30 yet thinner than 15W-40. Most wear happens at cold start and I don't expect a splash lubed motor to be any different. I'd expect the 0W-40 to more readily splash cold. I see that in the start up behavior, the gen stops shuddering faster after cold starts with 0W-40 than the other oils I used.
I thought the 10W-40 HM synthetic would be optimal but it did start harder at freezing. The shearing cause is unknown but may be related to being the first change after conventional oil and was affected by dissolving the remnants of the conventional oil. The 100C viscosity at 10.55 was still above the starting viscosity of typical 10W-30 of 10.2-10.4.
