http://forum.hunting.net/asppg/tm.as...1&key=󨁴
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.
The difference is more significant on high energy storing single cams like the PSE Carrera, Black Max, and Bowtech Extrem Solo. The numbers I got back then were in the neighbor hood of 1- 3 ft lbs over that same weight range.
I'm sorry if this flies in the face of what you thought you knew.