It is my belief you should have enough clothing with you to spend the night uncomfortably but safely at 14,500' for your summit attempt. If you get sick, conditions change or you get injure up high any less can put your life at risk.
When I did Mt. Whitney on about the same weekend in 2007. I took my 700 fill power 2 pound + down parka...and I was glad I did. The temperature at Trail Camp was low enough to put an inch of ice on our water bucket overnight. I don't remember if I took the -20* F or the 15* F sleeping bag.
My core clothing were...
Micro grid fleece top
Patagonia R2 vest
Arcteryx Power Shield Hoody
Marmot Sharp Point Gloves
The down parka was in the pack for the summit attempt.
You will need a wind protective layer. I used the Power Shield hoody and softshell pants.
Clothing wise this was like a winter trip.
Most of the trip to the peak were in the micro gird top. The temperature did not get over 40* F all day.
Do not under estimate your water needs because of the cooler temperatures. I went through ~5 liters that day...the last liter snow mixed with water.
