Last time I looked at WBIII was just after they added the Spitfire Mk XIV (hey, its my favorite WWII aircraft), and it in no way matched the British reports on it. It was slow, climbed horribly, and couldn't turn very well. That aircraft would never have been accepted for service given how much better WBIII's 1942 Merlin 61 Spitfire Mk IX is.
The FM on the Spit XIV was a joke.
The FM on the Mossie VI was pretty poor too.