Specifically I would like to know if the voltage regulators that are on Arduinos are linear or step down. I am currently powering my Arduino Leonardo with an 11.1volt LiPo, and I would be wasting over 50% of my energy if the Arduino uses a linear regulator. If I need to I can add my own regulator before the Arduino.
Linear.
Possible sub's:
5V http://www.digikey.com/product-detail/en/OKI-78SR-5%2F1.5-W36-C/811-2196-5-ND/2259781
Connect to 5V pin on the power header, not the barrel jack.
Maybe pull linear 3.3V regulator off the board if you don't want it running off the 5V. Add this external. If not using much 3.3V current, then live with it.
3.3V http://www.digikey.com/product-detail/en/OKI-78SR-3.3%2F1.5-W36-C/811-2195-5-ND/2259780