My wife has 21 165 pro I like the khaos setup better, just worried about the boost khaos being to much of a wheelie monster. That's the only reason I would put a 165 on it.Why don’t you just order it in a 165 and then put a 155 track on it for the flatlands. The tunnel length will end up similar to the current axys chassis and cooling will not be an issue. The 155 track and rails will also be cheaper to buy than the 165.