I went with the MLD Superlight Bivy as well - very awesome.
Mine specs out at 6.3 ounces.
CF bottom, M50 top, XL, Halfmoon netting.
I bought mine specifically for winter camping so I choose the halfmoon netting.
Last year (which was one of the colder years for the PCT) a hiker (Paul Bodnar) logged the temps every day, so it might be worth looking over those temperatures as you consider which option you consider.
The halfmoon netting can at times cause it to get a bit hard to breath. On a few trips I have had to keep my face right where the netting is.
If I were to be taking one on the PCT next year I would for-sure go with the full netting option. Than again, I would probably want something with more protection from the bugs-that-cannot-be-named than what a bivy offers. If I were to carry the weight of a full enclosure (which a bivy is) why not carry an extra 2 ounces for the sake of a much larger area you can get into, sit up in, and all that sort of thing, for the Sierra's where those flying creatures cause hellish nights. By the time you put your MLD SL Bivy together with a tarp (even a 9x6 cf tarp) you will be at the 9+ ounces mark, which is exactly where the ZPacks Hexamid is at. Just something to think about. This has been something I have gone back-and-forth on myself. I have owned both and I am just not sure which will be going with me...