King Tiger would win a "duel" vs anything short of the JS-3, which in fairness, barely made it into the closing weeks of WW2.
88mm L71 gun fired with a higher rate than the 122mm, optics are more accurate, it would score hits 1st at range and kill quicker than the others, as well as have the protection to stand and shoot. Its gun would kill any of the ones in the contest, even a Panther.
While the IS-2 was still trying to range, it would be hit. The 122mm gun had a very slow rate of fire, and was actually not as accurate as an 88L71.
....and its turret was not slower.
We are talking slugfest, yes?, not manuever, I would pick Panthers for my army, but King Tiger for a slugfest, assuming you started at say, 3000 meters or so.
The King Tiger was an expensive, complicated tank, and it was not for fast armored exploitation...but in a standing gun duel, it was a freaking monster.
...The JS-3 would win (if it were included) simply because its armor is too good frontally, even for a long 88mm gun, it would probably survive long enough to land hits on a King Tiger, and kill it around 1000 meters or so, after being hit numerous times 1st.
