I would highly recommend doing Shasta in a day to almost anyone. Especially the AG - it really isn't bad in good conditions. Maybe this will inspire....
We were hiking by 3 am. 2 hours later we were passing guided groups leaving their high camps. After another 3 and a half hours of scenic slogging we found our selves on top. It was 8:30 am - we didn't know what to do with ourselves.... so we lounged. At 9 or so we headed down. Once past the summit ridge we reached the obvious glissade point, so we hit it up. It was a bit hard but none the less it was fast. We were back at the car by noon - much earlier than expected. A 9 hour round trip day.
We moved at a decent pace but I'm sure there are many that are faster.
It could have taken us hours longer and we would have gotten down safely. Light and fast is the way to go - go get it.