I've flown the YakT ALOT this tour, its slow rate of fire cripples its HO abilities. You must only open fire when close, and if you miss with the 1 or 2 rounds you fire, well you won't fire more than 2 before he's past you anyways....
The 40mm will have a similarly slow rate of fire and when you add the convergence factor, there will be few HO kills committed by the IId.
As far as the Hurri IId penetrating the PzIV or Osty are concerned... ermm penetration tables indicate that the 40mm will have a VERY difficult time!! This also should apply to the 37mm on the ostwind AND the YAKT. The 37mm should only penetrate the PzIV from very close range and then only in the rear hull of the vehicle. The 37 and the 40 in aircraft though, should penetrate the top of the turret.
This information is easily located on the web, when I get home I will post links.
SKurj