RE: Fletching: Offset vs. Helical
Slightly due to wind drag which is why it's better for arrow stability, is it significant or relevant....no and the advantages certainly out way the disadvantages.
And to your other question in your first post/thread starter, I'm a right handed shooter and us a left offset. Right/Left shouldn't matter unless you use matching offset/helical bladed broadheads. The direction of spin is not relevant.