If you'd like to learn how to calculate the efficiency yourself, Palmer lays it out pretty well in How to Brew:
http://www.howtobrew.com/section2/chapter12-5.html
Here's the thread on Venturi devices. I'd definitely say that is your best bet for batches that size if you don't want to invest in an aeration stone.
https://www.homebrewtalk.com/f51/cheap-easy-aeration-gadget-68218/