Since you asked...some ideas, not that I would do everyting, but if you want to par ounces, perhaps it will give you some ideas.
Z1 Pack = 4.20 oz
* Joe has lighter options, can you use something smaller?
* XUL should not require strenum strap or waist belt.
* Could probably save 1 - 2 ounces.
Pack Liner = 1.41
* ZPacks lists a 750 cu in Cuben stuff sack @ .40 oz
Blue Foam Pad = 4.48
* GG 3/8" pad = 1.9 oz
GoLite Poncho Tarp = 11.00 oz
* MLD Silnylon Poncho Tarp = 8.8 oz
* Possible Cuben Poncho Tarp?
You asked about bivy -
* Yes, you have down jacket & Nuatek
* MLD LiteSoul Bivy = 4.40 oz
* no ground sheet needed with Bivy, so net bivy = 2.74
Easton Nail Stakes = 2.82
* (8) MLD Ti Stakes = 2.30 (use rocks, etc to help)
Capilene 1 top = 4.90
* replace with BPL Merino Hoody
* This replaces Beanie too
* Might no need windshirt as much (see below)
Windshirt = 3.17
* Use Poncho instead
Windpants = 3.60
* Not needed, wear tights
Sunglasses = .60
* not needed, unless snow (you have ball cap)
Digital Camera = 6.56
* there are lighter cameras
Notable missing - Poles for tarp?
* MLD has light carbon poles, or are you going to rely on natural replacements?