Well I'm not an expert...but I'll chime in. I've used all the options you mention above timberline and for an early season mule deer hunt I'd hand's down pick a single man, freestanding tent.
The bivi wouldn't even be a consideration for me, I'd gladly carry the extra 7 oz to not be stuck inside one of those for 24 hrs through a rain storm again. And trying to rig a tarp over it in a way that it won't get blown into the next county in a wind storm is difficult.
I used a tipi last year on my mountain goat hunt and while it worked great for the situation, it probably wouldn't be my choice on an early season above timberline hunt. I was hunting later in the season and knew I was going to be faced with cold, rainy, snowy weather and having a stove to dry out drove my decision. There are some draw backs that would edge it out for me on your hunt. 1. The nest adds too much weight and without a nest, condensation will be an issue (I know there are ways to manage it, but it will be an issue). 2. It is very dependent on stakes for a good set up and to be able to handle high winds. That can be an issue above timberline. 3. Even with adequate staking I don't think it handles wind as well as a low profile single man tent, at least not without a lot of flap and noise. I'm not trying to knock Tipis, I like them and think they have there place, this just wouldn't be it for me. I'm sure others will disagree.
I think your sleeping bag choice is spot on.
Freestanding tent above timberline on an early season mule deer hunt in CO
Tipi above timberline on mid season goat hunt