About when do you make the switch to the 5w-30?
Well 5 yrs is certainly a successful test I'd say. I have always had what I think is too low pressure so I used to run thicker oil. Then at one fall autocross, I didn't get the engine warm enough (coolant fine but oil just 120) and 1/2 way through the first run it shut off. I was lucky it just sheared the roll pin that located the gear on the dist shaft. An easy fix but I stopped using the 15-50 oil and went to 10-40 summer and 5-30 in the winter.