I like and use 5w20W straight petroleum based Valvoline oil in all my street builds under 650 HP, all out drag race motors or HP street motors over 650 HP I use Valvoline VR10w30wt racing oil, I quit using 20w50 and 10w40 Wt. years ago after testing them on a series of engine dyno tests.
As AndyF mentioned oil does two things in our motors, it lubricates and cools, 5W20 weight will start doing its job a lot sooner, building and flowing under pressure, than thicker mixes will