Get the large or the Xtra large. I used to shoot the medium because (like you) I thought that was the size I should use but I noticed that with a slightly bigger openingmy vane damage and noise were gone.

I shoot Beman ICS 340 Camo hunter arrows and I use the Xtra LargeBiscuit. My arrow only touches the blackbristles and fits slightly loose in the biscuit. I have found the best results when I switched to a larger opening.

I would say large or XL