A higher FOC simply makes your fletchings work harder is all. This could effect trajectory in a minor way because it may increase wind resistance over a longer length.

A lower FOC doesn't control the front of the arrow as well, so low FOC arrows tend to not do real well with large fixed blade heads. You can use a lower FOC, but it will require a better tune than an arrow with a higher FOC and better fletchings.

FOC is about the last thing I worry about in an arrow, but I don't concern myself with higher FOC arrows, like 15% and above.

The one thing to keep in mind, the more FOC you have, the weaker your spine will be because you have more weight in the front of the arrow. So high FOC arrow tend to be heavy if spined correctly.

With todays current technology in broad head design, fletchings, rests, bow design and the awareness of tuning I would say 9-12% would be a goal to shoot for. I think this would give most current archers with average equipment and skill a decent arrow to work with.

I wouldn't go much below 8% unless you have REALLY good arrows, good form a fair understanding of how to tune a bow. Adequate fletching would be a must as well. An example would be a newer archer with little tuning experience using a cheap carbon arrow, light cheap satalite large cut broad heads, and 3 or 4 inch straight fletched vanes. You would probably do ok with field tips, but when it came time to tune for broad heads it would probably give you fits.

I have seen people walk out of cabela's with this type of a set up. They shoot great in the back yard with practice tips, then wonder why they miss or wound game when they go hunt.

My opinions anyway.

Paul