I've been following the trip reports pretty closely and it looks like from the attire that I won't need some sort of 800-fill down jacket for this trip. I do plan on wearing an under armor shirt, flannel, then rain/wind proof jacket/fleece.
Do not judge what you need by what you see people wearing during a highly aerobic activity. You are going to need to be warm when the sun goes down at Trail Camp, where it gets awfully cold and windy...especially when the sun dips behind the Sierra Crest.
I was out this past winter in a blizzard where the temperature was 16* F and the wind was gust in the teens. The most clothing I had on while moving with softshell hoody and vest, I switch to a Gore-Tex shell and R2 vest after lunch.
I checked out last year's temperatures in the region for the period. Based on that you should plan on single digits temperatures at Trail Camp and to low 30s for the summit.
Just manipulate this url for past years info...
http://1.usa.gov/Jp8X9Z 
