Last Il-2 attack on GVs that I did I took out three Ostwinds. I did it by being very steady on the aim, narrowing my field of view to get a more realistic scale, and firing from beyond 1,000 yards. In each case I killed the turret, though the third one got me too.
Personally I am looking forward to the Whirbelwind as it will be less effective against the Il-2.