Not to your specific question, but some guidance that might be useful. I’m sure others will chime in on EE vs. K.
As a longtime resident of the Seattle area and backcountry camper in our local mountains (and Colorado mountains) I personally would not assume that spring and fall mountain temps are in the 40’s (coastal – okay). In fact, if I was in the PNW mountains, I would assume that temps are likely to be in the 30s or lower. I’d be grateful for a night in the 40’s. Others may have different experience.
I took my kids backpacking to Royal Lake in the Olympics in August (several times) and we had frost in the morning – temps probably were in the 30’s. Two years ago Camping in the Pasayten wilderness in mid September with snow and temps in the 20s (think north end of the PCT). last August, horse packing in the Pasayten in July @ 5,000 feet and it snowed and nighttime temps were low 30s or lower. I know this isn’t going to your question about EE vs. K, but it might help inform you about possible temps in the PNW and how that impacts your gear selection.
I tend to select my gear based on the limiting condition and how that limiting condition affects my survival or fun. As our glacier climbing instructor, told me years ago “I find that being too cold is a bigger problem than being too hot”. (Me, I HATE being too hot, but I tend to follow his guidance).
(BTW I love the idea of the open footbox in warmer conditions because I HATE being too hot, and I would probably buy one if I knew the temps would be 40-60, – in fact I did, a MLD Spirit 38 that can do double duty as an over-quilt).
I just ordered a K Alsek for similar timeframe to yours with anticipated usage in the PNW @ +5,000 ft and Colorado Mountains @ + 10,000. A Palisade may be enough for others, but I sleep cold – especially if it is a 35 degree fog and drizzle. And I have a selection of other sleeping bags.
