I putt on a slight arc based on my fitting at Club Champion. I found out that a face balanced to something really close is the best fit for me. Single or double bend necks are preferred, but can get away with a plumbers neck.
My guess is very little arc. I have always putted best with center shafted putters, and have found my happy zone with the face balanced Ping Sigma 2 Kushin-C.
How much is dictated by the type of putter you use?
I've been going between a Scotty GoLo 5 and my EXO 7 recently and have spent time with them on the putting green at the same time. I won't called the GoLo face Balanced but my arc is minimal when I put with it. Using the EXO 7 (24*), I find the arc is much more pronounced in my stroke.