My $.02:

It all depends on your climate and your "body temperature regulation" and what you like.

I see you're in Seattle. Lots of rain and "cooler" weather year round (as opposed to Ron in Arizona). I would think that a 13 oz would suit you for "year round" wear and that 16's would be nice for year round wear or at least 3 seasons (MAY be too hot for summer).

Body Temp Regulation: What I mean is that some people tend to always be HOT or they sweat a lot. These are the people that sleep on top of the covers in winter. ;) If that' you, then the 16 oz would probably be too warm in mid-summer. Depending on you climate (like Arizona), it may even be too warm for some other seasons or any day above 70 degree F. THAT BEING SAID, if you're skinny like Matt Newsome, you may WANT the extra warmth of the heavier wool even in a warmer climate (like the Carolinas).

What you like... if you can borrow someone's 16 oz kilt to wear for an hour or two, try it! See if you like it.

FOR ME PERSONALLY: I LOVE 16 oz (8 yard) kilts, but tend to wear them much more in the winter as I DO tend to be hot all the time and I live in PA... we have warm summers and cold winters. I wear my 13 oz kilts year round. I don't have any 11 oz wool kilts. My 11 oz PV kilts are great for spring / summer / fall and I sometimes wear them around the house in winter (why wear it out in winter when I have a 16 oz wool?).

Now if you want to get into 5 yard kilts, I would say 16 oz fabric HANDS DOWN, but I DO have some 13 oz 5 yarders that are nice as well...