I agree with previous comments that you can tour pretty light in weight and volume. Ultra light gear helps, a good example are down sleeping bags vs synthetics, a winter synthetic sleeping bag, even compressed, will take a full rear pannier. However, ultra light gear is not the answer, what it really makes the difference is your philosophy of traveling and how good you are at feeling comfortable and self-sufficient just carrying a few things.
When solo-touring in South America along Carretera Austral I saw two North American lads on carbon frame mountain bikes carrying only bar and saddle bags and their tent tied to the handle bar. They were riding as hell between villages, relying on daily accommodation and food supplies. That is not my way of touring. I like to enjoy the scenery, nature and be self-sufficient on water and food for at least 3 days, so I can wandering around if I want to, without any urge of resupplying, cycling emptied stomach or asking for water to the odd passing by truck.
I also agree that you need pretty much the same gear for a 3-day trip than for a month tour, in many of my trips food and water are the heaviest items of my load. I always try to reduce the number of pieces of luggage and loose items on the bike, the less pieces the easier to set the bike every morning, move the bike and luggage in buses, trains, trucks, wade streams or small rivers, you name it. If I want to be light I can easily tour with only two rear panniers and a 20 l dry bag. In the dry bag I carry a solo tent, mattress and a down sleeping bag. In the panniers: a small dry bag with clothes, a mesh bag with small items (knife, torch, sewing kit, tooth brush, water bags, ...), a mesh bag with a cooking set (spoon, gas or petrol stove, depending on the country), and still plenty spare room for food and extra water, and that is pretty much all. I tie the 20 l dry bag with 3 elastic cords along the length of a Thorn rack, so I can open the panniers without having to remove the 20 l dry bag. I do not use bar bags, as I like to keep my handle bar clear of gadgets (only a tiny basic computer) and see the front wheel, and I dislike anything attached to the tubes (bags, pumps,...), or loosely attached to the bike, or rattling inside the panniers, other than bottles in their respective tube holders. If I need extra carrying capacity for very long trips, winter touring or desert crossings, them I use front panniers on the Thorn low loader, but I never use handle or tube bags. With that kit I feel self-sufficient and comfortable.
I believe that with your Thorn RST, carrying 17 kg and being well organised you are well set for long and exciting trips.
