This book gets into the day-to-day operational life of a Russian
P-39 squadron. It's an excellent reference of life outside of the cockpit, and yet still let's you know that the P-39 was more than competitive against Me-109's & FW-190's. The point isn't stated exactly, but the reason they WERE competitive is that combat on the Russian Front was generally below 15,000 ft, and never above 20,000 ft. Remember, neither side was using high-altitude, long-range stategic bombers, it was all low-level tactical aviation.
Still, the book doesn't get into the airplane specifics I would like, i.e. . . how specifically it was better than the 109/190, or even how it compared to their own MiG's, Yak's, LaGG's.
The point is, it's a great book on the operational use of the P-39, and is worth reading.