Hi Steve,
I think the head wear pattern problems caused by different stock formulations is one that hasn't received the attention it deserves. I have to admit it took me a while to figure it out as well. It really became apparent, though, when working with magnetic film, which has a base thickness that varies between 3 and 5.5 mils thick, and a very different head wrap depending on the base thickness and base type (with the triacetate base being stiffer than polyester).
John French and I spent quite a bit of time trying to sort this out around 10 years ago, and the only solution we could come up with was to have two sets of headblocks, one for 5 mil acetate base film, and a second for 3 mil polyester. It cost a 'friggin fortune! (And then there was 5 mil polyester as well, just to complicate matters further).
As good as 35mm full coat magnetic film could be, I have to admit that I'm more than happy to not have to deal with it much any longer (except for archival work). On the other hand, I recall hearing some 6 track score masters for various pictures over the years that would just blow away most multi-track tapes. Part of this had to to with the thickness of the oxide, and part of was due to the track width, which is wider than that of a 24 track tape. I know more than a couple of scoring mixers who really lamented the move away from film. (Of course, many of the recordings that Bob Fine and Bob Eberenz did for the Mercury and Everest labels were recorded in 3 track 35mm, which, with an equivalent track width of 200 mils, could (at least theoretically) produce a recording that would only be equaled by at least 1/2" 2 track tape).
--Scott
