Pro-stock cars run 0 and 2 weight oil for a reason! They don't want to give up any power or leave anything on the table. Those running 0-40 Mobile 1 should know that it is about a 35 weight or one of the lower viscosities in the 40 weight spectrum, so not quite as bad.
I run half 0-40 Mobile 1, and half 0-20 Quaker State Ultimate Durability. Both are in the top 10 in Rat540 blog to make the best 0-30 full synthetic blend IMO.
I've tested 30 and 40 weight oils back to back same day testing on an old stock RX-1 and the difference in performance was HUGE. I went from beating my buddies 800 Doo to getting outrun by it. It just did not "have it" running 40 weight oil, I could tell it just lost a step and racing my buddy confirmed my hunch was accurate, I surly lost some power with the thicker oil thru pumping losses. Came back home switched back to 30 weight and the performance came right back and I continued beating up on my buds 800 Doo again, neither one of could believe it, but he was right there with me and could see I changed nothing but the oil, I didn't even bother to change the filter for time constraints, we just wanted to see how the oil change could have affected it so much. I'll stick with 0-30 if thats what the manual calls for, there is no advantage to running thicker oil than need.
Rat540 blog here and it's good reading and awesome test reports.
https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/