The limiting factor is the MOSFETs: they have a maximum current rating, maximum power rating, and limited Safe Operating Area (SOA). (The SOA limit involves both power and time.) A fan can help with the power rating and SOA.

The motor limit is dependent on the timing, gearing, and load-- for instance, a FWD car draws less current when the wheels spin. It is possible to blow an ESC even with a motor with more turns than the ESC rating.

My advice is: don't push it. Get an ESC that is extra hairy, so you have a safety margin.