It's been cold, but it hasn't been freezing lately up on the mountain. In fact it has been in the low 50's to upper 40's lately.
Check http://www.wrh.noaa.gov/mesowest/timese ... C1&num=168
for the temps during the last seven days near the upper tram station.
That link shows the temperatures at 8600 feet. If you camp higher the temperature drops by about 3 to 5 degrees per thousand feet.
Keep your eye on the weather forecasts to be sure a cold snap isn't arriving at the same time you are and you'll probably be fine in that bag.
I'd agree with Myth that having a good insulator underneath you is at least as important as the sleeping bag. Feeling the cold ground beneath your hips and shoulders can really make it hard to stay asleep.
As for me, I sleep cold, so I always make sure that I have an extra warm layer for my evening clothes, in case I need to put them on during the night. Plus a warm hat and gloves.
Have a great time!