Not been in a Spit unfortunately but have been in the back of a P-51. An amazing experience from start to finish, total of 3 hrs or so across two days. Loved every single second, it pulls very nicely, still does very capable aeros (while I fought the urge to make dugga dugga dugga machine gun sounds) and sounds and looks wonderful and I felt very privileged to have done it.
The owner also has a T6 and a Sea Fury, and says the Mustang is a pussycat compared to the Fury.
It is a beautiful machine, but I would still take the Spit.