This was supposed to be a picture thread, so here's a sort-of lightweight setup I put together. I haven't toured with it yet. Except for my down sleeping bag and cat stove, there isn't really any ultralight gear in there. I saved weight by leaving a bottle cage, rear brakes, front derailer, pedals and air in the tires behind.

I plan on adding a small front rack for the sleeping pad or tent, or both, to free space for a bigger camera, tripod on top of the Carradice and most importantly, food, which is the only thing really missing. There's no lock either. I plan on using this for short 3-5 day tours. EDIT: just thought I could roll the pad without folding it and strap it to the top tube.
I will still use 4 panniers for longer tours even though I can easily fit everything into two. I actually put all my gear, including tripod and front panniers in the rear panniers for air travel (plus a carry on daypack, used as handlebar bag). I still prefer using 4 panniers for better organization and weight distribution, plus I don't want to have to cram my gear in all the time. The other thing is food. On longer trips, I don't want to have to find food in small packages every day. I want to add more backpacking during my tours and that means I have to carry lots of food sometimes. On my last trip, I went on a 5-day hike, biked 2 days to get there and another day to get to the next town after. That's 8 days. I found out at the last minute there were a cafeteria and small store at the base of the mountain but it wasn't cheap and the store had very limited choice so I still had to bring lots of food.