Not exactly an answer but... Given old HW robots used Bosch 750s - so 750W of power - provided what you choose has more than that then surely you have a good drive mechanism. Its not like the old HW's were slow or anything. Tornado ran 750's on 36V and was like a missile. So anything modern with more than level of power should do fine.

If you could find an ESC that would cope then running a pair of HK4035's or HK5020's would be more than enough power. Yes they are expensive but if you want all out power then you get what you pay for, and if you treat them right then you should have no problems with them.

Going back the multiple brushless set up, Dave told me that the dual set up in 360 was a little pointless as no two motors were identical so eventually the weapon would only be driven by one motor as one would be more powerful than the other. So you would end up with the same issue but worse!