If they used the ROQF 75mm then it was just a bored out 6lber firing U.S. 75mm shells. It was identicle in preformance to the US M3 75mm, but (IIRC) it had a slightly lower rate of fire.
And the Churchill was perfectly capable of damaging and even killing a Tiger, I was just refering to that specific incident. It tickles my funny-bone that the tiger was reported destroyed, while they could still fire the cannon, the machine guns, and drive unhindered, all they would have had to do is just had to knock the shell out from under the turret, and they would have saved the Reich somewhere between 400,000 and 800,000 Marks (depending on sources).
As to the LW amunition, I think there has been an argument against HVAP/APCR rounds for US and German tanks on the grounds that the rounds issued to both nations' tank forces were relativly scarse, and developed, again, relativly, late in the war. If the 6lber gets APDS, then my panzer gets APCR.