I'm hiking the AT (early start) this spring and probably the PCT next year and I wanted a great bag/quilt for both. I chose the Sawatch. So far I haven't done thorough testing, but I would compare its warmth (when properly sealed, with a hood or down baclava) to my marmot helium at a weight savings of 9oz. Its a true 15 degree quilt at 25 oz (long). Thats only 4 oz more weight than a summerlite (L) and whole lot more temp range. I haven't used a nunatak alpinist, but seems like most people are layering more at these temps. Aaron says the sawatch is designed to be comfy in base layers at 15. I've found this to be true so far. I'm 6'1 175, back and side sleeper and it fits me fine. Just FYI, I have heard some complain that its not wide enough though.
Here's my reasoning for going for a 15 or 20 degree bag or quilt over a 32 degree. Obviously this is just my 2 cents and related to my own hiking style. I like to hike for most of the day. I aim for a quick start with meals usually had during short hiking breaks so I don't do a lot of hanging out at camp outside my bag during the coldest hours. There is more efficient warmth/weight in a few extra oz of down in a sleeping bag/quilt then in full on puffy camp cloths. The bag can also be worn as a garment around camp if needed. For short and fast trips, I don't mind sleeping a little cold, but for longer trips when my energy gets more depleted and a full nights sleep is more important, those extra oz really pay off. Seems like plenty of people get away with a summerlite or 32 deg quilt on the PCT, so in the end probably either would work.
Will review the sawatch when I get through those first cold weeks on the AT....
have fun on the PCT and let us know what you decide!