I shoot a 70lb set up and my arrows are carbon rebels- 5075, blazer veins, and 100gr. sonic heads. Using the "Front of Center" formula my arrows come in at the 8% range. The formula says that carbons should be in the upper area of the acceptable weight dist.(7% to 14% I beleive) for proper Front of center. What if anything should be changed if my arrow flight looks great??? Are these the proper spine arrows for 70lb??

Depends on your draw length, arrow length,and bow (yr, make, model). More info and one of us could run it on a program to give you a ball park idea.

I shoot a "05"bowtech justice, 29in draw length, and 281/2 in arrows (291/2 with broadhead)

You won't catch me shooting a broadhead in that range. I don't care how my field tips fly. When I'm shooting at deer, the wind blows, twigs and grasses get in the way and I what maximum penetration on bone glancing hits. High FOC gives a "forgiveness" factor in these areas. If your arrow spines properly, there is no upper limit. I'm currently shooting 25% FOC out of my compound. Flight is perfect, especially in brisk winds and at long distances, when others arrows would be planing off line. Very high FOC arrows are a big advantage in most hunting situations.

How do you get a high FOC % with the proper spine and arrow length?

There are programs out the Archers Advantage, TAP and On Target that will do most of the hard work for you.
Just put in your bow info and what gr head,arrow lenght, nock and fletchyou want to use and they will give you a list of arrows that will spine properly.

But you are not going to get high FOC like SA and myself unless you go to a heavy head 200 + grains, altho you can get there with a 125gr head but you will have to use 100gr brass inserts.

You'll probably have to go to the next higher spined arrow and go with 125 gr tips to get an FOC in the 12% range. with a 125 gr tip on my 7595's I was at 12.8% with a 28.25" arrow but underspined for my 30# DL.

I couldnt imagine what the arrow must weight if the head is 200gr and you want correct FOC????

You will be surprised the arrow is not that heavy 494gr's my FOC is 24.8% while I have perfect spine for my bow.

I've been with Russ when he's done all his test.. it works, I am getting on the high FOC program. You guys can't even imagine the penetration and stable flight. I'll never go back to 125 gains again.