I'm in a similar predicament, but only with a firestorm instead.
I've run both the 5700kv and 4600kv from castle and both motors run extremely hot.
I have a 1509 in st-e and can't praise neu motors enough unfortunately the blitz is based on the firestorm so any 15xx series neu won't fit as the can diameter is too big. The 14xx series will fit but it only comes in 5mm shaft size-which limits your pinion choices.
The 11xx series doesn't fit due to the motor bolt spacing being too small.
Since medusa are no longer in the equation i think a very good option is the velineon.