CQB M15a4 Proline Setup?

[Raguri]

Right then, due to the shop in HK being out of stock for ever on G&P Rifles, i have decided to upgrade my currenct one!
So then, what do i do exactly to get a decent ROF setup, without overkill on the spring etc. (So i dont loose consistancy in fps).
I was thinking about the following motor, the all new G&P M170
But, what would i need? Already thinking of a 12v batteries/11.1v Lipo's.

However, the technical part is where im stuck! Do i go for hi torque/hi speed gears, etc etc.
I have already sent a message to a gun tech asking about it, so hopefully he will reply soon!

But until he does, what do i need?

Or do i buy something which is falling apart, and upgrade that entirely?
(Mp5 or similair!)

EDIT: Will also say, this is NOT the cqb version, it is the full length. I want to convert it into a cqb gun