My overview of the Mamba Max 5700

[captain harlock]

I mean the motor and the controller wont work as effecient as they are supposed to in a lightweight T4, B4, Touring cars or pan cars or even an electric 4wd buggy.
The nitro stadium truck you have is specifically designed to handle the power of nitro engines. The drivetrain is thus heavy and sturdy and your 5400 motor was wrongfully chosen for the conversion- its for electric rigs meant to go head to head with their nitro counter parts. You need a much lower KV of a highend motor.
I dont have any experience with the Neu, but since they do have segmented rotors, they're up for the job. They're very popular and powerful as well.
As for the Lehner.. I would choose the 1920/9 or 10 turn motor.
The Kontroniks are good for your case, too. You can either get the Twist33 or 37 or go for the big Kontronik FUN500-27 motor ( same dimension as the Lehner and Mamba Max), but with 5mm shaft.
The Lehners Neus and Kontronik's big motors were actually made to replace a nitro engine in a heli or a big air plane and get a performance as good as a nitro engine or slightly better.