I really think it matters on what kind of 65-70 liter pack you are carrying. If you are rocking an Alice pack, that shit is going to hurt after a while.
I have a 70L Osprey Aether, which is specifically designed to carry heavy/awkward loads for long distances over multiple days, and I have loaded that thing down for long hop outs. Like 2 gals of water, a 12 pack of beer, handle of vodka, and premade foods. I think at one point I was carrying like 80 lbs across portland/eugene. I had problems with my thighs and knees, but not anywhere where the pack was contacting me. Lots of padding and adjustable straps.
But then again, I've been firefighting and backpacking long distances in the wild for a long time before that, so it does have a lot to do with physical conditioning.
My first hitching trip I carried a 75L that was over 80 lbs. I soon learned, as others have pointed out, to drop shit along the way that I didnt need.
Seriously though. Invest in a good pack, it could be the difference between you doing this for a long, or very short, time.
I wish I could carry less gear, but I travel through multiple different elevations/ecosystems in the winter, so most of my weight is cold weather gear and liquids.