What’s the temp rating on this setup

Are the Patagonia merino bottoms long johns? If so, and you use wind pants, I would wear them together and chuck the 100w fleece pants. If not, I would look for something like miltary surplus power dry or Power Stretch bottoms. 100w fleece is halfway to nowhere, IMHO — all the weight and none of the warmth.

I would keep the Ultra 20 too and take it on your shoulder season trips. It's hard to cover 3 (never 4) seasons with one bag. We all like to have the lightest gear lists, but the reality is that cold weather busts the SUL budget pretty quick— compared to summer lists anyway.

I would look at the bivy like a windshirt. It has to add warmth and another layer of weather security and helps keep a quilt tucked in. There's 25F and then there's 25F and blowing 30MPH, where the bivy would really be an asset. Imagine lying there all night with visions of the bivy hanging in your gear locket at home :( It's your call on condensation and weight issues and whether you like sleeping in one in general. A backyard test session is in order I think.

Good idea on the rain pants. I have a prime pair of Golite Reeds that need to be worn. And yes, the Patagoina pants are full length long johns.

I'll always keep the Ultra 20, but trying to create a sythetic sleep system. I was hoping the EE quilt would handle 40* alone, 35* with the bivy, and 30* with the bivy and puffy. Also, it looks like the EE quilt has 4.0 Climshield and is rated for 40*. Last year it think the same quilt was rated to 35*. I'm just curious what people with experience with think.