did you find one Stefano? check out this
Arc'Terix pack.. it's a bit large but if they make a 70L I'd look into it... super comfortable.. it's on my dream list..
and yeah, be smart when you're on washington.. beautiful but can be deadly... check out franconia notch (E. side, the flume too) if you have the time... super views and you could make a day hike of it.. always keep an eye out for escape routes.. there are many there...
have fun and i hope to see some pictures and your impressions..