By the way, here's a technical question.  Of what nature is the HE round for this 75mm gun.  Some might not know, but one of the very common sorts of anti-tank round used for decades is called (by the British at least) the HESH round, or High Explosive Squash Head (I kid you not).
This was a relatively thin-skinned round filled with a plastic explosive.  On impact, the explosive would spread out (ie: splat) over the surface of the armor, and then the fuse would detonate it.  The pancake of explosive on the outside of the armor would create a shock wave through the armor plate resulting in massive and catastrophic spalling of metal from the inside of the armor plate into the rest of the tank interior, f*cking it all up good.
It's entirely possible, depending on the nature of the B-25's HE round, that this same kind of effect could have been accomplished, at least on thinner armor plate.  I wouldn't immediately count out this round as a tank killer just because it's an HE round, untill we find out more about it.