The Clark TK60 can handle 3s (~12V/60A) so it should easily push powerful motors.
However, you can probably go fast enough with 2S. We had a meeting today and a friend brought his HL Panther with WH board (new Chinese brand) + DKLM PDSG gearbox (fast gearing) + 2S Lipo.

That thing was insanely fast while retaining the legendary torque of dual-clutch gearbox at climbs. It was so fast that I think if it goes any faster you will not be able to control. It achieved at least 100km/h scale speed.
Also keep in mind that your M18 is a lighter tank and will likely go even faster. I am going to get the fast PDSG for my under-construction Tammy Leo1. I already have the medium speed one on my Centurion.