BL-Revo, I would reccomend it for a touring car or maybe a 2wd buggy, but I would bet your 4wd buggy would be too heavy. Maybe if youre only using it onroad it would be ok. Mine never thermals, but it does run hot, even with a fans on the motor and esc (140-150 on both). Not to mention it makes more power than you could ever use off road. Really it makes more power than should ever be in a touring car, my TC3 is running a lola body and a handmade lexan underbody/ front splitter/ rear diffuser just to try to keep it on the ground. It will spin all 4 31mm foams with no effort at all.
As for the motor rpm limits, I dont know enough about this to comment on the efficiency of my set up, but someone who works for castle posted on another forum that the mamba 4600 system was perfectly capable of running 4s lipo, that it would be within the rpm limits of the motor. The only problem is the esc wouldnt be warrantied.
I think there is a lot of middle ground between what is most efficient and what a motor can physically handle. Ive run my mini t with a mamba 6800 on 5s lipo, and it works fine, it didnt even need a fan on the quark 33 while geared for about 60. Thats 119k max motor rpm. I know, I dont expect that to last very long. When I replace it Ill probably aim for about 1/2 the kv it has now.