I agree with some of of your thread, but a 600 anything I'd run a STEEL CRANK. As far as the small bore/small valves they are on the right path to produce TORQUE. Plus the flame travel across the piston is less meaning less chance of DETONATION. More torque in some way offsets horsepower at the lower and midrange of the rpm scale.
"Stupidity is Ignorance on Steroids" "Yeah, it's hopped to over 160" (quote by Kowalski in the movie Vanishing Point 1970 - Cupid Productions)