Factory fletched vanes are typically a 1 degree offset blazer vane or something very similar. These should provide decent stability with a fixed blade head, but a little more angle makes can improve accuracy. I like 2.5-3 degrees offset or helical. The rotation averages out any asymmetries. Less rotation will make the flight more sensitive to arrow and component straightness. Iron Will broadheads should shoot as well as any fixed blade head with your factory fletched arrows since we have tight tolerances on concentricity. With whatever head you choose, spin all your arrows and make sure the tip spins true and does not wobble. This is always important but even more so with only 1 degree offset. Good hunting!