Castle does NOT say that 4S is not ok. What they say is that 4S is out of spec. The deal is that the internal bec of the MM can only handle 3S (and not very well IMO), so you'll have to disable the internal bec and use an external one. Just remove the red wire from the harness that plugs into the receiver. I run all five of my MM controllers on 4S. In fact, none of the MM controllers that I have now have ever seen anything less than 4S.

The 4600 on 3S is the best deal going for all around running. With the 4600 you can go to 2S for a nice controllable track setup, 3S for general bashing with very good speed, and 4S for "OMG something's gotta break" speed. I've found that with MOST MM controllers cogging usually isn't a problem. If it cogs, it's overgeared.

Whether the 4600 on 4S is controlable is subjective. What one finds controllable, another might think is out of hand. Personally, I think that the 4600 on 4S is stupid, but in a good way.

The 4600 on 4S geared for any sort of real speed (over 55 or so) is going to get hot. On 3S, you can likely run all day. A friend of mine has the 4600 in his stock (save for upgraded tranny) emaxx and he runs it on two 3S 6Ah packs. He runs an integy heatsink/fan on the motor and doesn't have any heat problems. As for runtime on the 12Ah setup, most times, he doesn't even bring a charger out with him. By the time the batteries are gone, he's ready to pack it in.

I believe the MM 4600 system to be the best of the line. It is the most flexible and the fastest. Just don't go too nuts on the gearing.