The biggest problem will mot likely be the IHS because it is not plane in most cases and further, the interface is low temp solder that has a much lower conductivity than anything else in the therml path. We have experimented with fully liquid immersed chips as well but we need cooperation from the chip manufacturers on that front.

That's the main reason why I really don't want to say anything about the final junction temperatures that we can achieve ... it'll depend on the specific chip in question ... not even the model