If you go with a R/C hobby BEC add a small 5 volt fan on that heatsink, they are designed to to have fairly constant airflow over the heatsink, think heli's and airplanes fast moving cars.
Lastly if you plan on using a dedicated servo controller later make sure the output wires will handle your maximum amperage. If not you will have to change them out. I use a Castle Creations 20 amp for my bot, and it is nice and easy to switch wires, I am not sure why they don't come with 20 amp capable to start with.