I found this snippet from the Hiram Walker research department on experiments started in 1949 and published in 1959 entitled the "Effects of Barreling Proof on the Ageing of American Whiskeys". It revealed data on an 8 year project for entry proofs of 110, 118, 127 and 154. You can read the first page if you click the increase image size. http://pubs.acs.org/doi/abs/10.1021/jf60103a008

This research was probably not inconsequential as the Federal regulations for barrel proof entry were then at 110 proof and changed to 125 proof in 1962. Note it states an "industry-wide experiment is now under way". Others here have posted that even though the regulation changed in 1962 the increase towards 125 proof didn't really start till the early '80s and may have then been driven by other revenue deregulation of the industry