Lowest BSFC is usually obtained at peak torque output. This is true. However this is usually measured at WOT. At part throttle you introduce pumping losses. You still have a torque curve at part throttle but it usually shifts a bit to the left. So your peak torque RPM is usually lower. BSFC and fuel economy in a car are not the same thing. In a car the slower you can turn the engine and still have a comfortable acceleration available, the better the fuel economy is going to be. Dodge Vipers cruise at highway speeds at 1200RPM or something. My old BMW 328 does it at 3500RPM and still gets 30+MPG from a 2.8L.

The logic is to use WOT in the range of the engine's best BSFC. This might be 500-1000RPM +/- of best BSFC. Gearing and everything else comes into play.

Hemi's are no longer the best. They haven't been for a long time. 4 valves pent roof chambers are ideal and most common today.