zx5 - ready for more power, but what motor?

[rociduro]

I have a ZX5 rtr version, but I've upgraded all of the drivetrain parts over the last few weeks - ceramic diff balls, steel outdrives etc. Now very bored with the pace of the stock G20 motor. Thinking about Mamba max power, but seriously, what is the sane choice? I want to be as fast or faster than my mates gas car (kyosho Inferno) around an 1/8 track, but would also like some sort of driveability retained... I mostly bash, but want to get into some racing down the track.