RE: helical or straight vanes
Try shooting your broadheads with straight vanes. If they fly straight and group well at various hunting distances, then go with the straight. If you encounter erratic arrow flight and grouping, try the offset. If you still encounter erratic flight and groups, you may have to use the helical.
In my past experiences broadheads tend to plane with straight fletch a cause innconsistant grouping, especially at longer distances of 30 + yrds. Putting a spin on the arrow with helical helps counter the planing making for better arrow flight and grouping.
Noise with helical fletching may be something you have to give into to get accuracy. I have never bowhunted elk, but the noise from the helical does not seem to cause misses when shooting at whitetails.