Gibbs is a good product as well as others, you can do a search.
The LIGHTEST
oil that works in your engine. Like Dan said clearances are a big factor.
I would like to know why KC recommends 50w
oil.
If your engine has good pressure with a lighter
oil I would start there.
I have heard hydraulic lifters perform better at high rpm's with a heavier oil (stability) but this may not be your environment.
I've tried 30/40/50. My temps [oil and coolant] were cooler with 30 and pressure was good, so that is what I use.
Try out a few