I suggest the Osprey book on P-39 Aces. It covers the Soviet use. One of the more interesting findings in that book is that when later Soviet built fighters came out, such as the Yak-3, Yak-9, and LA-5, the P-39 units did not transition to those seemingly more advanced aircraft but stayed with the P-39.
And as Tomo said, the 37 MM gun's antitank capability was slim to none, being designed for air-to-air. The RAF did tests and found the 40MM guns fitted to Hurricanes for use in North Africa would crack a captured German tank. The USAAF urged them to try the P-39 for that role but the RAF found it would not crack a German tank; they also found that the ejector rod was too long and the 37MM would jam after one shot - they had to saw it off in order to do the tests. This is in the book "Druids' Circle" about RAF armament testing in WWII.