Sleeping bag rating for spring ski touring in PNW?

I'm headed out in early May to the PNW and British Columbia for some ski mountaineering like the Forbidden Tour, Spearhead Traverse, etc... whatever the weather lets us get away with.  I figure this trip is a good excuse to upgrade my older, heavy synthetic fill sleeping bag.  I'd like to go with down for light weight and packability.  I have a ultra light bivy to cover the bag if moisture seems imminent.  My question is what rating do folks lean towards for spring (late March through May/June) ski touring in the PNW?  I was about to pick up a 5F Western Mountaineering bag but fear I'll be sweating a ton.  I'm generally a warmer sleeper.  I'll be using a thermarest or thin closed cell foam pad.  And using a tent or floorless shelter.

Any advice appreciated.  Thanks!

I've been using a 35 degree F Western Mountaineering Highlite bag for a few years and it has been great. Weighs only a pound. I've even done some winter trips with it. I might not use it for a high bivi on Mt Rainier, but it's been fine for general spring trips in the Cascades.

ditto.... i've used a 30 degree down bag for spring touring for the past five years and that bag combined with all my clothes and a decent down jacket has worked fine for just about everything except high camps on rainier.

My 25 degree F synthetic Marmot Pounder Plus serves me well enough(in concert with my lackluster synthetic belay jacket, warm hat, gloves, socks, etc.) through almost all of the year with a ~5/8" Evazote pad. I sleep warm in general, but shiver more than a little as the temperature drops below ~25ish (with the aforementioned fashion accessories on inside the sleeping bag). My bivy sack lets me push a little lower in temperature too.

I've been very glad I've had a synthetic bag.

Yep 30 is the magic number. I have a Mountain Hardwear something or another- not real name (synethic superlight 30deg) that compresses into nothing - it only has 1/2 zips but....

I also bring Mont Bell puffy pants and jacket to sleep in too (weather dependent of course) or add a down jacket if the temp is going to be questionable.

Sweet tour - Have fun.

I use a 30 degree feathered friends half bag and a down jacket. Most the time I use the jacket as a blanket. it weighs 18 oz and packs down to grapefruit size and the down jacket is always in my BC pack.