I had been debating about going 8.5t from 9t. the heat was definately from the gearing. since your loosing 300kv, u should probly try gearing just a tad taller to get it back. maybe even taller since its a bigger motor. go for 5.5-6.2 FDR.
I run my 9t at a 4.74 FDR for about 10 mins of shi** and giggles in a open parking lot.
I wonder if the 8.5 could take it longer since the car happens to be just the speed i want.