[IvanK]

"What we have now is a Spitfire that can match the 109 in a dive."

BS.... go on line and prove it. See if you can hold the same distance from a 109 with both of you performing the same manoeuvre. You have the 109 Maintaining its ATA and RPM with the Hurris and Spitfire both having RPM rapidly drop to <1600RPM and Boost dropping to zero. The 109 pulling combat power and the Hurri and spit pulling stuff all !

If you don't want to go On line then replicate the manoeuvre individually as best as you can starting from the same IAS hold the push for say 15 seconds and then note the IAS ... both the same ?

In the brief tests I have done here are the results. Using the Quick Flight Over Dover as the start point.

BF109E3 Wait for prop pitch to get to the 12 O,Clock setting.
Start from 200Kmh select Max Max ATA
At 300KMH Push progressively forward until 90 degree nose down is achieved over a period of 8 secs
Increase in IAS achieved 100KMH
Av acceleration 12.5KMH per second

Spitfire IIA Prop Full Increase
Start from 100MPH
Select Max Boost
at 140MPH Push progressively forward until 90 degree nose down over a period of 8 secs
Increase in IAS 20MPH
Av acceleration 2.5MPH per Sec

So the Spit gets around 2.5MPH per second and the 109 around 15.5MPH per sec.
Or the BF109 gets a round a 50MPH gain over the Spit in the manoeuver ... hardly "staying with the 109"