I don't think you need to buy any more heads but the 125 will weaken the spine which if there isa spine problemit sounds like a weak one and the 4" vanes will offset the 125 head. I can't see how you are getting the arrows to fly left and right, should be one or the other. If the bow is tuned and the arrows are fine then it's either you or contact or a mechanical problem with the bow. You should be shooting just fine if all is well (not all heads fly crappy. The mussy's and mangus don't). The 340 @ 28" with a 100 head at your weight I would say is fine-stiff, but that should not be causing the wide fluctuation.The only thing I would buy is some new shafts. At your poundage you may just be shooting the spine out of them (you did say that they never did though, so maybe it's not the shafts). Most guys don't shoot all their arrows all the time. Maybe you should get a new dozen and onlypractise with 4 at a time and keep some fresh for when and if you think this problem isoccuring again. I don't think you need to buy anything else unless something is busted.

A well flying FP means something but not everything. A BH will tellus if itall is as we think it is and it's saying your a little off in your assumptions.