Here is a thread with some actual speeds and arrow weights I shot back when I first got my Allegiance, well before this discussion came up. Calculate the KE of the 345 gr arrow vs the 360 gr arrow. You'll get 80.94 lb-ft vs. 80.86 lb-ft. The lighter arrow has more KE. A small difference to be sure, but real nonethless.
See, this is what I am talking about. This doesn't prove the 345 grain arrow will out penetrate the 360 grain arrow. It also doesn't prove that 345 grain arrow will out penetrate a 400 grain arrow from the exact same bow.