Hpi hellfire ss

[obelix]

I am finally ready to order the Motor, esc for the hellfire build but I need some advise.

This is the setup I was looking at getting
Mamba Monster v3 Running 6s trackpowers 25c
NEU 1515 2.5d
std gear ratio 13t mod 1 pinion 53 spur


I do not know all the gear ratios to enter in Brian G's speed calculator so I based this on the rpm I would get from a 28 nitro engine (35000) and increased it slightly I also selected this motor because RC Monster has It in stock.
Is this a good setup or can I get better ?
Does anyone know if there are aluminium diff cases available for the hellfire if not which other make would fit.

Thanks