I personally like my arrows around 15% FOC or a little more. One thing that's come up recently though, arrows with a "Built-in" FOC. To me, these are a waste of money. Any decently made up arrow is going to have a decent FOC. Basically, the "weight forward" arrows have just been wrapped, or camo'ed at the front. Pick an arrow, add a point that is roughly 1/3 the weight of the shaft, and you'll be really close to that 10-15% that's recommended. As for spine, I do think you can be overspined, but it's pretty hard to do. It doesn't cause tuning problems for the most part, but a stiffer arrow is a heavier arrow. No reason to drop your speed when you can get the right spined arrows, or just slightly overspined.