Aaron, since I know you're capable of getting yourself out of trouble, I'll reply to your points with the intention of perhaps informing others.
"A down vest doesn't keep you warm in rain. This is what the 19 ounce quilt does."
I also have a homemade 19oz down quilt built from the TH kit, including an M90 shell. While Paul makes some strong claims about M90, I wouldn't trust it as a bivy. That's why I take along a silnylon tarp - an extra 10oz. Last year, I was between Langley & Whitney under perfect skies @ around 11.5k, but decided to stay in a clump of (stunted) trees, rather than push on 400 yards to exposed granite. I still put up my tarp, even though I like to sleep out. In the middle of the night, some monsoon flow hit with all the works. Lesson: always have the tarp at least ready.
However, my quilt is typically wrapped up tight in my (homemade) compression sack & shoved into the bottom of my pack, with my BV450 sitting on top, and then the rest of my clothes wrapped in a turkey bag at the top of the pack for quick access. I can't think of a situation where I'd want to be digging through all that to get my quilt to keep my warm if I was holed up for an hour or so waiting out a T-storm. My layering system would then be: vest, windshirt (I have a Houdini), then poncho/garbage bag.
It might be me, but I'm getting colder these days as well, so even though my quilt is good down to 30, the vest helps had another 5 degrees or so. My down vest weighs 10oz, extra weight I don't mind carrying. So, now I'm up to 20oz extra, but I'm pretty confident I can comfortably hold out against wet & cold, night or day.
"If you get in this situation, (south of Forester), you don't stay put anyway.
How is setting up a tent and getting in supposed to help you in lightning? You keep moving."
Maybe I'm just sensitive to lightning. If you can stay warm & keep moving, then go for it. But the chance of getting hit doesn't leave any margin - it's pretty binary, yes/no. So, the idea is to find some cover, pull out your pad, put on your poncho/garbage bag, and wait it out.
As for the comment, "stupid light", it really is apropos in the big scheme of things. Here's a for instance: as everyone knows, we had another low snow winter in the Sierra this year, so a lot of water sources are either dried up or highly suspicious. Typically, I've just drank straight up without filtering, but sometimes used tablets.
A few weeks ago, I was using full tablets between two 20oz gatorade bottles just to make sure each bottle had enough time to do its thing. So, instead of carrying 1 container of 16-20oz of water, I was now carrying another 20oz at all times. There's my tarp+quilt weight. Even worse, I took along an empty 1L platypus that I actually ended up using through some sections where there weren't any (good) water sources. So, know I'm carrying 2-4 lbs of extra water, which is blowing out all my SUL attempts.
Last, but not least, even though I'm extremely careful planning my food, I still had at least 16oz *too much* food. Add all this up, and I'm carrying somewhere between 4-5lbs of extra weight - in this context, trying to save a few ounces on important weather gear seems futile. But the funny thing is, I really didn't notice carrying the extra weight. It's not like it's question between 45lbs+; rather, it's the difference between 15 and 20lbs, 4lbs of which is nothing I can control due to the water issue.
Stupid light: skimping on stuff that has a very high utility to weight relationship.