There have been threads about this, but the auto engine management in the first Spitfire (and afaik, all Spitfires) given to the player in the GB Campaign is horribly wrong. After takeoff it's impossible to get decent speeds out of it, maxed throttle & level flight gives varying top speeds, sometimes as low as 120, never over 200. I'm being outrun by bombers and it's essentially made the GB campaign unplayable past the point you're given the Spitfire.
Needs fixing asap! (and please don't say use set CEM to manual, some of us don't want to!
)