The trend these days for hikers is a move towards ever lighter gear. It is, I must say, one I completely support. I hate that feeling of hitting the trailhead and slinging on a backpack that is crammed with everything from a stove and mountaineering tent to a big sleeping bag. A bag like that weighs 15kg or 20kg and you feel every gram of it when slogging your way up a mountain. It is just so much more pleasant when going on a day hike to shoulder a very light little daypack with not much more than some water, a few snacks and some warm clothing. That little thing is hardly noticeable on your back and you just move so much more quickly and easily.
The guys who favour super-light hiking all want to get their pack weights right down. My totally unscientific rule of thumb is that a pack of about 5kg or less is barely noticeable on the trail all day. I don’t think I would move very much faster without it than I do with it. Remember, this is hiking, not ultramarathon running. If I was running then even 5kg would slow me down. When hiking, however, that kind of weight makes no difference to a big guy like me. Heck, I carry more than that on my beer belly as it is.
The next step up is a pack of about 10kg. This is often more or less what my day pack for mountaineering comes out at once I’ve thrown in water, food, extra warm clothing and an ice axe. If you are reasonably fit and in good condition, carrying a weight like that without any real problem or without being slowed down too much. But it is once you start going above that weight that you will find you are working considerably harder on the ascents and also moving more slowly, even on good terrain. The difference between taking a pack weighing 10kg or so and one weighing 15kg or so if often the weight caused by carrying a tent. This is the reason that many people who now go on extremely long distance trails are opting to ditch their full tents and instead go for some sort of shelter or tarpaulin tent that weighs about a third as much. These are great for low level hiking. But if you are going into windy and mountainous terrain you will have to bite the bullet and carry a full blown tent. The only other alternative is a bivy bag, which will protect you from the elements but will not be comfortable at all.