I've been running the Mamba 7700 in my Bj4WE, just put in a Novak 4.5 today to test it out.
Both are fast, but there are subtle differences, which can be somewhat customized through ESc and trans programming.
with both systems set at defaults, no expo on throttle
Novak is punchier off the line. Mamba kicks in a little later. Mamba has a higher top speed. Also had to cut out a little of the chassis to fit the Mamba, since it's can is a little longer than the Novak.
The Mamba will notice if you roll backwards (like if you spin out around a hairpin), and pause until the car stops before letting the throttle kick in.
the Novak goes when you tell it. Not a big deal, but you have to be aware of it. (hello sensorless)
I think the best scenario is the Mamba ESC, and any brushless motor. The programmability of it lets you set it however you want.
the 5700 will be probably be fast enough for you, or the 6.5.
personally, I like having all the power of the faster systems, I just learn to use the first 3/4 of the throttle. Use the last 1/4 only when needed.