As best I can figure the stock titan would be in the 3100-3500kv range

A 10.5 would be in the 4200kv range
A 13.5 would be in the 3600kv range

The brushless system will be more efficient than the brushed motor (and more durable).

For an endurance race speed isn't everything. Keeping the car on the track and in one piece is the main focus. A 13.5 will allow you more runtime between pack swaps and have less stress on the whole car.