I go with helical myself, not sure how many degrees.
It's the Bitz helical clamp.

I'm compiling speed data right now, in fact. It's not my primary concern, but if I'm going to make choices that sacrifice speed, I want to know how much I'm giving up, and how it affects my trajectory.
I'm checking 5" vs 4", offset vs helical, feathers vs vanes, and several different weight shafts.
I'm a doubting Thomas, and I need to see it for myself.
I figure if I'm going to be sharing info with other archers, I want to be speaking from my own observations, and not just repeating what I've heard.

With what I've seen so far, BG is right on.
Two indentical arrows with 4" feathers (one helical, and 1 offset) shot exactly the same with the chrono right near the bow.
For that matter, the 4" helical vs 5" helical shot with 1 fps of each other.

Don't worry about the 1 or 2 fps downrange. Keep those BH's steady with the offset.
(I'm even considering helical because I release with fingers and want more forgiveness in case of a bad release when my hands are frozen.)