Have you emailed PTG to ask them about chatter? The large spiral does look like it might be the smoothest operator of the bunch. They don't specify which cut reduces the most weight. Curious myself, I want to order one for my M7.
I haven't asked them because I doubt they have much experience cycling the bolt over a full magazine. I have talked to them before about reamers and other stuff and they were very helpful but I think they are machinists and not so much shooters or hunters. I wouldn't worry about it with your model 7. I haven't noticed it much with my short action factory TI's but my TI 30-06 is a little raspy.
