Craig, I have always mixed my lye baths with 2lbs per 5 gallon.
Now the caveat... 
1.  make sure your container can handle the weight of the iron + liquid.   I use BRUTE containers, and have a hanger system to retrieve pieces. (So I never have to reach very far into the solution)
2.  Never ever try to move a Lye Bath that contains solution.
3.  When working with my Lye Baths I wear Chemical Gloves (not dishwashing gloves) AND a Full Face Shield. Protect those eyes! if a large piece I might pull on a Vinyl Apron also!
4.  I keep an 'active' hose at my feet, just incase an emergency rinse is needed. 
 
 