RE: Helical vs. Offset
Four years ago, I went to the PSE shooter's school at Creekwood Archery, just outside of Brockport, New York. The instructer was George Chapman, who will forget more about archery in a day than most of us will learn in a lifetime. Anyways, George told us about a test he did with three differently fletched arrows, one fletched straight, one fletched offset, and the last one fletched helical. At 20 yards, there was no real world difference between the offset and helical, but both of those grouped tighter than the straight fletched arrows. He then went to some insane distance like 90 yards, and his findings were quite eye opening. The straight fletched arrows were garbage, the offset were something like 20" group, and the helical was under 6". This of course was done with a shooting machine to test just the ability of the fletching, not the archer.
For the past several years, I have used 4" helical feathers, and I don't think I will go back to anything different. They seem to stabilize very well, and my broadheads, Steelforce 100's, group right along side of my field points.