more warmth or less weight

What date will you be going up?

If your going soon, a down sweater will be nice around camp and if your party stays a while at the summit. You could be below 20 degrees at night and the summit could be the same low.

http://forecast.weather.gov/MapClick.php?site=hnx&smap=1&textField1=36.557&textField2=-118.275

Wait, WHAT?! Your going up in trail runners? Fine in summer but right now it's mountaineering conditions!!

So assuming your going in summer your fine. I would even cut back on the sleeping bag and think about a bivy/tarp. Get lighter socks, wear shorts, etc.

Like the op said, it depends on when you are going. If you are planning on going before Aug of this year,, then it really is a mountaineering situation. If you are going prime time Aug/Sep, your list looks good except for a few items:

You need some kind of parka/jacket in case it gets down below 25 during dinner or breakfast;
Consider taking a ccf for additional insul – you may want to shoot for a +4 R value;
Take some head gear;
Think about a light day pack for the summit – it is 2 up and 2 back from trail crest. All you need is around 3-4l of water and some snacks.

Thanks for the comments. I'm going August 2nd. I guess we don't know yet what that really means. Crazy year.

Is a buff enough "hat" (with a Sun-Runner atop) for August?

Depends on your other gear. If you wear the driducks as a windshirt, the hood should cut the wind the 100 wt fleece of the buff should keep you warm. Also if you have another insulating layer with a hood you'll definitely be fine. If you're still concerned I would suggest the merino buff (it's doubly long so provides a lot of insulation but I haven't gotten to test mine in the cold yet) or the cyclone buff. The cyclone has gore windstopper and has kept my ears toasty on the Rim of the Grand Canyon in the dead of winter. Also kept my head warm on some frigid windy nights in the single digits in town without any hood or other head gear.

If you're looking for a good down jacket I would recommend the Montbell Down Inner with a Hood. It weights 9oz and will be considerably warmer than a 200wt fleece (feels about same as a 300 REI fleece I have…before putting on the hood). This piece will also fix any concerns about the warmth of your head gear.