Yep, Pro-Stock cars run straight 0 and straight 2 weight oil for max power, but you better have the proper clearances and oil pump for it too. Thicker oil than needed will rob HP. Higher viscosity does not provide less wear, just higher oil pressure and pumping losses.
I wouldn't run 0-20 in a trail sled designed to run 0-30 however, I know I wouldn't run 0-40 in it either. Put it on a dyno to see the difference. Keep in mind there are some lightweight 40 weights and also some heavy 30 weights, you have to really look at the spec.
The best wear protection and top rated oils for wear in Rats testing is 0-20 and 0-30 oils. Here you can read for hours.
https://540ratblog.wordpress.com/
You only want thicker oil weight if you have large clearances and/or a weak oil pump. All that maters is the boundary layer of oil holds up between the hard parts so they don't collide and weld together, anything beyond that just robs power and slows you down.