SU152, not ISU. Although we might see the ISU too, who knows.
At the moment the bigger HE shells should actually do some damage to tanks. But keep in mind that the largest tank shell are only 88 mm and even the largest artillery is 105 mm. 152 mm will deliver quite a punch, I would say.
As an ISU and ML 20 expert, we can safely say that anything up to a tiger tank is pretty much ruined when hit by a 152.4mm 43.3KG (containing 6KG of explosives)
Tiger tanks, for example, simply lost there turrets when a shell hitted the frontal hull armor. Soviet SU/ISU 152 doctorine was that the crew had to keep firing at the enemy tank untill "It did not looked like a tank anymore"
As for the KT, there are reports of them surviving direct hits..
Well for the tank, not the crew.
If your tank survived, your crew was dead anyway
The reload time was something between 1 to 2 rounds a minute
As for the AP and APHE shell, i sorry vonmudra, but the trajectory was the same. Muzzle velocity of the HE-Fragmentation, steel OF-540 shell was 655 M/S, and the APHE BR-540 was 600 M/S
EDIT=
Forgotten Hope
I think tomorrow is a good time for a news update? Who's with me?