540 burnt his motor's out as the magnet was just too much, and geared too fast for the size of the motor. It's fine going off that chart that tells you 30A is fine, but thats not realistic for for more than just driving around.
As soon as you slamming forwards and back, that burst current will shoot right up. Also when you underneath someone with their extra weight giving more grip will shoot that current rating up. 540 needed LOADS of power to stop and change direction due to all the grip, and the motor's just couldn't take it.

If your running without magnets there's not much to worry about on this front - get a decent lipo such as OptiPower of the new thunder power 65C packs (pretty pricey these though) and work from there. With all that power your more likely that the motor's can't hack it rather than the rest of the system if they're particularly small in size.