The real question is WHY do you need a large pack? Most people take way too much stuff and end up ruining their trip with burdensome luggage. Learn to pack light. You are a tourist, and generally people will cut you some slack if you aren't attired in your most spiffy coordinated outfit, changed daily! I am extreme, I know, but managed six months with three changes of clothes, (double socks, I wear two pair to cushion my feet more). For me, basic black was no problem. If you need to, throw in a blazer to dress it up. Or a sweater works well with a tie, and doubles as warm clothing under a jacket or windbreaker. Everything was hand washable in a hotel sink, dried on the radiator or on a clothes line. My main problem was I needed room for painting supplies. Now THAT was hard to cut down!
Women can do it too, but usually have to manage more stuff. I have seen many women who were experts and had everything mixing and matching, they always looked like they had a different outfit, changing accessories, etc.
You will look better if you aren't exhausted lugging stuff around, and will enjoy your trip more too. Consider purchasing some clothing over here. It makes a great, special souviner ("Yeah, that is my Basque beret, I purchased it in Pais Basco!. . ."). The world doesn't end at the US border, it BEGINS there. People manage just fine with local clothing! Besides, the gawdawful reach of US corporations means you can purchase you Dockers anywhere now (actually I like mine!).
Take less, and enjoy your trip more!