Ok, from opening up, on WEP as it lasts..
Full fuel load, fuel burn as in TA which is faster than RL
5 minutes left my Spit XIV at 18K, for 20 it was some 5:45
A RL Mk XIV should be there in 5. I think with the same boost.
Note, that both the IX and VIII boosted will be 45 seconds faster to the same alt than our AH XIV, - but in RL equal.
Of a +25 boost mk XIV, I do not know the performance.
One must also bear in mind that AH WEP has limits that were not there in RL, - you could basically push your Spitfire throttle through the gate and keep it there as long as it went. There were examples of Pilots that panicked and ran on full WEP for something like 30 minutes without harming the engine.
Anyway, 109G2 from AH, 9700 feet in 3 minutes, in 5 mins at 17.6, and in 5:50 it hits 20K.
Not sure of the boosts of that one in AH, but I guess 1.42, and that would leave it like a minute too fast.
So, we have a perked and PORKED Spit XIV