All that is true, but as some have already noticed it's the track that ultimately decides. Some tracks simply do not allow lower turn motors to come into their best efficiency range unless geared down to a point where you can't take advantage of their rpm, so you're back to square one. Off road even more so since grip comes into play and no matter what rpms you pull, you just can't make it stick so it's useless.
But for the initial poster, be careful with brushless. In the long run they win cost wise, but you have to be careful. If geared incorrectly, they go up in smoke a lot quicker than brushed motors, and then it's another 300$ (a speedie) or about 100$ a motor. A lot of people can tell you their story of woe (if only they would admit it).
Lipo is the same. Be careful with the batteries as they don't have clearly visible markers to tell + from - and reversing the wires in the heat of the race costs a speedie again. I dunnit.