It really depends on how you feel at Long Lake or CL#3.
When I'm in good shape, I can make it down to Lower Rock Creek Crossing and have no problem reaching Lower Soldier Lake when in fair shape. My preference is Army Pass for Langley.
The only problems I see is having enough clothing for the cold, wind up at the pass and ability to sleep at 12,000' to 12,300'.
If you decide to stay low, there is a lot of exploring options to fill out the day.
