Royal Purple and Amsoil are fine oils, but at $12 - $13 a quart locally are just not in the running. Too many good oils available - and for me, I run what Ford recommends and that's their semi-synthetic Motorcraft at about $3 a quart. Previously, it was all Valvoline. If you have a flat lifter engine, Brad Penn, Joe Gibbs or Rotella. The weight - why 20W-50? Do you have a full out engine or just a mild one? If it's a mild one, 10W30 or 40 should suffice. Thick oil and windage/splash wont help horsepower