Well, I think as far as carried weight goes, that depends on how big you are. 48 lbs wouldn't be a problem at all for me, but for someone half my size, it might be. My pack weighed about 30 lbs when I went, but I would bring more water next time so it will be heavier. I brought 3 quarts but used almost all of it climbing up to around tree line and back. Next time I'd bring a gallon. Larger size also means that more water and food is required.
My thighs were feeling the burn as well last time I tried to climb. I don't know a whole lot about that but someone told me that it's due to lactic acid buildup from exerting yourself far beyond what you're accustomed to, as was the case for me. It was easy to ignore it and continue on, but I'm sure it's much preferred to be in better physical condition to begin with.
Summa sedes non capit duos