The KI will own the P39 with ease, its only constrained by black out from what I have seen.
BTW
first time I have spent some real time at 5000m plus in IL2 was flying the pony vs 109 and vis versa. The graphics for that game at high alt actually suck bad. Why the space blue noncense.
Flying at 15000 feet looks nothing at all like that.
The hit animations on the B17 look like they copied them right from gun camera film though..but the sky and ground look silly..