[Bluebottle]

The problem with the 1C SpitIXs in speed terms is that they are all modeled on the F model - even the LF. If you note the heights at which the supercharger switches they are all the same, apart from the 25 and the HF. Even the VIII is the same. The supercharger profile looks like Oleg used Merlin 63 numbers. The LFs should be a Merlin 66, which would be faster low down, then worse up high, than the F. The 25 is definitely not the same engine model as the others, but unfortunately that extra performance coupled with the energy retention make the Spit 25 the contentious plane it is.

Once 150 octane fuel became available (in the RAF in Europe that was early 1945) all the Spit IX sqns over there were modified.

I hope one day someone will do some new slot IXs and LF IXs with a more realistic FM and the correct engine performance model