Now the point is that Soviets decided to give their limited amount of 100oct fuel to certain P-39 units, most probably because they saw that to be the most effective way to use that stock. P-39 units participated the battle of Berlin and many top Soviet aces got most of their kills while flying P-39s.
At least some, for ex our second ranking ace Wind, Finnish fighter pilots saw I-16 and I-153 more dangerous opponents to Brewster B-239 than Hurricane.
Juha
That might be so. The P39 had very poor performance and it made sense to optimize it. The fact remains that the performance figures given here:
http://www.ww2aircraft.net/forum/attachments/flight-test-data/109542d1256053432-russian-fighters-
for the Spit V and Hurricane II are without 12lb boost while the other fighters are using boost levels possible with 100octane fuel.
Here's an estimate of a Hurricane I performance with 12lb boost:
http://www.wwiiaircraftperformance.org/hurricane/Hurricane_Speed-HRuch.png
and you can see the P40/P39 no longer seem so superior.
OTOH, here the performance of the Spit IX:
http://www.ww2aircraft.net/forum/attachments/flight-test-data/109541d1256053432-russian-fighters-
is shown with 100 octane fuel boost levels and is a very close match to RAE figures.