Just for reference on MOD1 gears, the Lambert gearboxes on Gabriel that have the big Ampflow motors driving them, with the big and I mean BIG wheels 900mm diameter have first stage MOD1 and second stage MOD 1.5 these are a standard gearbox which is not nearly as good as an epicyclic (sun and planet) style gearbox.
so MOD 0.6 for the first stage and MOD1 for a second stage should be OK if you don't go silly on the power!
Remember when dealing with drives for combat robots, the limiting factor it the GRIP of the tyres. you can have mega power slides that look cool but that alone doesn't win fights. if you keep the power of the unit equivalent to about 1.2Kw brushed that will be enough for most applications. if you want another Brutus just have 4 of them!