I need to wait awhile before weighing him again. Last weighing was about 8 months ago and he tipped out at 9.5lbs. Who knows what he weighs now. I'm sure he lost a bit from his turtle-soup narrow escape.
I wear extra large gloves and a size 13 1/2 wedding ring. When I pick him up my fingers don't touch around his carapace. He was the size of a silver dollar when I got him, his brother, and his sisters.
Don't know how high the temp got. After changing out 1/3 of the volume, the temp dropped to 92F. As I said in the OP, there was steam coming off the water surface when I added in cool water.
He made it overnight. Won't feed yet. Put a banded bunch of live anacharis in his tank to graze on if he wants. Not leaving any foods that can decompose since the high temps likely killed off the BB.