Have fun Tom. I've got a Flash 65, and it's an extremely light, reasonably comfortable pack capable of hauling a lotta gear. Once you get it loaded with weight, you'll probably have to monkey around with all the higher adjustment straps to be sure the pack is pulled as close to your back and shoulders as possible. With 35 pounds, even an inch can make a huge difference in how you feel with the weight.
The only drawback I've found with this pack is the ability to strip out the back support frame and turn it into a smaller, lighter summit sack. On REI's video it looks easy. It ain't. I've only done it twice, backpacking on Whitney both times, but trying to wrestle that stiff frame out of the zippered pouch (and then back in again) has been a major PITA. I actually bought a Flash 15 summit sack last month so I wouldn't have to ever do this again.
I haven't done Meysan yet, but have looked at it as a backup in the past if no Whitney permits were available. As I recall it's a little over 3000 feet of gain in less than 5 miles, but pretty much direct with few switchbacks - so fairly steep going. Meysan Creek will be to your left, but not very accessible. I think Grass Lake, just prior to reaching Meysan Lake, is your first easily-accessible water, so call it 5 uphill miles for your water needs. I'd take at least 4 liters of liquid, between water and -Ades.
Gonna try to tag Mallory or Irvine?
Watch out for the killer grouse that almost had Laura for dinner a couple of seasons back - it may still haunt that trail . . .
