Thanks for posting this, Camber.
Your SL data for the IIa squares with what I got for both online and offline ie 290 mph IAS +/- 2 mph. Where my data began to diverge (offline vs online) is when I climbed to 5,000 feet and 10,000 feet. The online Spit IIa begins to seriously decline in IAS while the offline Spit IIa holds a fairly steady IAS right up to 10,000 feet (and possibly higher -- did not test beyond 10K).
I can't fathom why the two flight models for the two same aircraft should be so different at emergency combat settings ie. 2800 at full overboost. (The needle goes off scale on the boost gauge, so I can't tell if it's +9 lbs or +12 lbs -- or something else for that matter).
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