[null and void]

Now sure about the dry vrs wet, a mile thick ice cap sounds kinda wet.

Ah, but a mile thick ice sheet doesn't continue to pour into the crater until all the heat is absorbed converting it to steam.

A wall of ice surrounding a red hot crater is much more benign than a wall of ocean encroaching on a 60 mile wide geyser of live steam.

With liquid water, the heat is fairly quickly transported to the atmosphere as steam, water vapor, salts, and sea bottom ooze swept into the mix.

Ice OTOH doesn't transport the energy planet wide, the crater ends up radiating most of the heat out to space, limiting the damage to the local vicinity.

[jpsb]

sounds reasonable, but alot of the ice would melt(fast) and pour in (but not like ocean water). One other thing, this cater is 200D miles and the gulf crater 60D, seems like a lot more energy (but can't say for sure without knowing density).

The major difference I can see is one hit near (relatively) the equator (better mixing) and the other at a pole, I would guess that if major impact caused extinctions this impact should have caused at least an extinction in the southern hemisphere.