Batman,since having some shoulder problems,I started playing with some lighter weight bows and heavier arrows with higher FOC.Dropping bow weights from 60-66lbs.,To 50-55 lbs and increasing FOC,I have been able to double my penetration.
I was playing around recently with a chronograph and after checking speed of a 714 gr arrow,I tried a 619 gr arrow from the same bow.I gained 10 FPS from the lighter,619 gr arrow.95 grs lighter arrow weight gained 10 FPS.
That surprised me,so I tried a 530 gr arrow from the same bow.That drop in arrow weight gained me another 10 FPS.That all figures out to: dropping 15 % arrow weight gains 6% in speed.That is just on my bows but I checked it over and over again.
Losing 10 % speed can't mean much in terms of trajectory.I have no interest in measuring all that but I know,the adjustment from 500 to 700 gr arrows was not nearly as big a deal as I expected.
The bottom line is,I wouldn't take anyone's word for any of this.It is very easy to assume what may or may not happen,but it is a very simple matter to try a few different setups and see what results you get.
I have had no problem adjusting to the heavier arrow weights out to 30 yds.I cannot,in good conscience,shoot farther than that at big game.If you can shoot accurately at further distances at game,the heavier arrows may be problematic.