When I was dragracing the turbo, I used the Kendal 20-50 - back when it was the formulation I believe is now cooked up by Brad Penn. The price was right and it worked well for me.
I would change it when shifting became sticky. Yes even with an air shifter you can tell a difference.
I continued to run this oil even while I worked on a racecar that was sponsored by a synthetic oil manufacturer, but today would be a different story.