[TinyTim]

"Hmm ... what is the difference between a Spit F IX and a Spit IXb. "

There isn't any its a nomenclature stuff up from imprecise authors its in the same vein as ME109 versus BF109.

When they use the term "stopgap" they are saying it was rushed in to use before the VIII. The VIII was already in development to replace the MKV but would take time to finesse and get into service. The IX was basically a MKV airframe with a new engine, some were actually converted MKVs. This stopgap turned out to be so it became a production model.

That's true, but it's worth mentioning that MkIXc as we have it in game has a Merlin 66, while IXb (or F) sported a weaker Merlin 61. The IXb/F was a true stopgap, IXc wasn't - it flew in large numbers till the very end of the war and even after.

It's probably a well known page to you Waggel, but worth mentioning anyway in my opinion:

http://www.spitfireperformance.com/

Can prove helpful for FM.

Thank you for all the effort Waggel, appreciated!