looking at an incubator or another brand for my wbbb xlc. What is the best fill weight for the bwca. I like to go in may, june, sept, oct. Will I notice a major difference in temp ratings?

0 degree? 20 degree? 40 degree? Full length is my plan at this point unless there is a reason not to go full length. Canoe camping so a little weight should't make a difference here.

20 degree seems appropriate but will I regret it? Thing is I will probably order two at the same time so I want to be happy with my purchase.

thanks

overfill? what is the reasoning for overfill? how much is optimal to add? is it worth the cost?

I think the 20 degree is the best all around. You can always vent the UQ. What I like to do is have one UQ with different TQ to match the temps, but I always end up going with my ~20 degree UQ, ~20 degree TQ and a old fleece sleeping bag I use as a TQ. This setup gets me through temps from 70 to 10 degrees.

In mid-August, I've experienced BWCA night-time temps in the mid-thirties. In October you can easily get ten degree night-time temps.

In August I bring my twenty degree U/Q. In October I bring that plus another twenty degree three-quarter U/Q and combine the two.

how much overfill should be added? What difference does it make. Looking at ordering an incubator 20 probably. I see a lot of people add overfill....should i? and how much? why should I or shouldn't I?

20* is my workhorse rating for most situations in the most time spent in conditions where that rating covers the most broad range of temperatures. This goes for my bags too.
I did a review here of my Incubator with a 2 oz overstuff. I got the additional 2 oz not for insulation, but more for proper and uniform loft.

I have had it down to 9* comfortably.

*edited for link to review thread
http://www.bwca.com/index.cfm?fuseaction=forum.thread&threadId=579842&forumID=347&confID=1

When I began looking at an underquilt the temps I planned to use it in was the big factor in my purchase. I trip in mid-May when temps can get to the mid teens so I went with a 0* UQ plus 2oz overfill. I also had it lengthened from 77" to 83" for better coverage. I can always loosen it in the warmer months for better air flow. On top I use a 20* TQ that keeps me warm in the cooler temps.