[Big-Foot]

The sintered disks engage and release very quickly which is why they are preferrable for racing applications. Right now, I think your issue might be in the hydraulics yet. Measure the travel of the throw-out fork when cold and hot to see what the delta is there, if any. Believe it or not a difference of .030" on the end of the fork will make a big difference in the way it feels.
Temporarily adjust any freeplay out of your slave cylinder to throw-out fork and see if that works better when hot as well.
I'm not a big fan of aluminum flywheels as they tend to "grow" when hot as well.. There are other reasons I don't like the aluminum wheels as well, but have found that the discussion of them is akin to discussing religion.
You may have multiple things working against you here.