After a few hours of sleep, I did some more testing.
This time I compared 218.4 to 214.1 (my 213 had a bugged film viewer

)
All tests made in Pony D, 6 gun version, 50% fuel, FB 0, same base for takeoff
Ground acceleration 0-100 mph: no difference
Level flight acceleration @500ft 150-350 mph: no difference
Dive acceleration: To reduce pilot error, I used autoclimb. Speed set to 400mph. Climbed to 10K, shut engine. When speed fell to 200 mph, I engaged autoclimb. Noted time to 300 & 400 mph.
Result: No difference.