For this argument, set the base speed of the transport at 165mph. You are then given a choice, knowing you will be flying into areas where you are likely to encounter hostile things such as La-7s, Spitfire Mk XVIs, Bf109K-4s, P-47Ms and Ki-84s, of taking a dorsal mounted 13mm machine gun and a beam mounted 7.92mm machine gun on each side or you can have an extra 70mph.
So, do you take the 165mph transport with the three guns or the unarmed 235mph transport?
Why do you take the one you chose?