I have the 10-ply Labonville competition chaps. They are heavy and bulky, but probably not that much hotter than the 6-ply ones in actual field use. If I had it to do over again, I'd go with the 6-ply. In fact, I might get a lighter pair anyway. The 10-ply are way overkill for regular use IMHO. And.... they're heavy and bulky.
I called Labonville the other day and spoke about the subject with them. The call was prompted by a Google search that yielded a hit for an AS thread (
http://www.arboristsite.com/labonville-inc/62383.htm) from a few years ago. Some guy wanted to know which ones to get (6-ply or 10-ply) and Labonville recommended the competition chaps for him considering the saw he had. Turns out he only had a 5100 (50cc saw). If the 10-ply were needed for a 50cc saw, then what would you use for a 90cc saw? Or more to the point, what saw would the 6-ply chaps be appropriate for? Anything? Drea from Labonville (sponsored forum) neatly dodged the question later on in the thread. Forum consensus was that they like to recommend their most expensive chap... even for a small saw.
So, anyway, the guy I spoke to (didn't get the name) said that the 10-ply are recommended for hot saws because the saws get, well...
hot. At least the bars do. Gives extra insurance during the "heat" of competition. Basically, for most purposes, 4-ply ain't enough but 6-ply will stop just about anything... as long as you get the Labonville ones. ;-)
I might still go with the full-wrap for reasons mentioned above. Besides protecting the Achilles tendon area, they will stay on the front of your leg better if you get hit by a running saw. The chain will practically pull them off your leg while it is jamming up with Kevlar thread, and may not stop in time before the leg gets exposed. Chaps should be adjusted to be snug enough to not move easily if you get hit, but loose enough to not bind or inhibit quick movement. Nothing would be more tragic than protecting the leg but getting whopped on the noggin with the whole tree because you couldn't get out of the way in time.
As for length, it's not an inseam measurement, it's the entire chap length. I have embarrassingly short legs and the shortest ones fit fine, so I think you guys with normal size legs need to measure from the belt line to where you want them to hang and get that length. You don't want them too long if you get the full-wraps, though, or they will surely bunch up at the knees once you strap them to your ankles.
As far as a 60cc pro saw barely touching the Kevlar? Watch this video from Labonville.
http://www.labonville.com/videos/v2.htm
Another good video I've seen from Madsen's website has them cutting through a ham and then a chap-covered ham. Watch it if you think you want to go without them.
Bottom line? Get the good Labonville 6-ply and be done with it. Bailey's has them on sale right now for under $60.