Cutting an engine won't help you with anything except torque (unless you're in a P38, then you create torque). This has been debunked several times...
Dropping gear will cause drag, even in a P47, and will slow you down. I'm not enthusiastic about F4Us doing it and I'm even less enthusiastic about aircraft that didn't have high speed rated gear using this method.
That said, a certain well known P47 from AH in the 56th dropped gears in a fight when he was close to augering in a stall fight. Instead of crashing, he bounced off the ground and got a reversal on the attacker. Gamey yes, but funny as hell.