"the compound shooter in me says speed kills and velocity is the begining of kenetic energy"
First of all, I think you should forget about what the compound shooter says in you. Your not comparing apples to apples if you try and compare what you are doing with a compund versus a longbow or a recurve. There are alot of different opinions on this subject, so let me give you mine.
Alot of bowyers will not warrenty their bow if you do not shoot over 8-9 GPP. I would use that as my "guide". I personally belive that a heavy arrow will give you more penetration. I shoot the weight I do (750 gr)because it keeps my bow quiet, and it hits hard. My mind is used to it and I see no reason to change.It is what works for me..
Although I have heard that 10 gpp is the perfect combination of speed and penetration. I still shoot what I feel works the best for ME. When I was starting out with traditional I did alot of expermenting with differnt arrow combinations, until I found what works the best. I wasnt worried about a flat tradjectory because I dont shoot game out of my "comfort zone", which is 20 yards. Do what works best for YOU and just shoot and have fun. I found out that ounce I got to this point I just made, its all up to you to practice, and to train your internal computer..
I believe in keeping it simple, and I leave the math out of it. It doesnt matter to me that arrow "A" will give me a "X" amount of more velosity, then arrow "B"... Have fun, and keep us posted