The problem with 10w-60 is it's as thick as some gear oils. This causes oil drag and friction. A decent synthetic 10w-40 or 10w-50 (if modded) is all you'll need.

We've Cosworths rallying on Silkolene PRO S 5w-40 with no ill effects but gaining the benefits of the lower viscosity - More power, better consumption etc....

Cheers
Simon