David -- That method makes a lot of sense, but I'm not sure I'll have much in the way of drybags on this trip. That said, maybe just wrapping the pack in garbage bags and tying them off will do the trick. It's not a wide river and there's gas station where I can toss the garbage bags in after I cross.
Nick -- I'd love to go that light, but budget is definitely a limiting factor right now. I should be able to get my base weight under 8 lbs, though. I'm going to aim for 2 lbs of food per day, and will probably carry a liter of water on average, so that's 16 lbs starting out. I can make that work.
As far as speed goes, despite being 6'2", I have trouble maintaining a speed of much over 3 MPH without doing a mild jog on at least a few of the downhills. That said, the terrain where I usually go hiking and running can be a bit technical, with quite a few ups and downs. The trail I'm planning to thru-hike is not necessarily flat, but it's much more gentle. I'm trying out a good chunk of it on Monday and Tuesday, so it'll be interesting to see how fast I go. I don't plan on running much on that trip.