In November of last year, I rode the front range of the Rockies. I had two rear panniers, a frame bag, and a drybag strapped to a front rack. I also brought a backpack (mostly because I liked the backpack) and ended up strapping it to the rear rack, which worked in theory but was messy in practice.
Here's the setup:
That didn't work. I was heading East on a 96-miles-with-no-services highway during a windstorm. The tailwinds were absolutely mind-blowing; I was coasting at 25, downhilling at 40. The road was clear and open, so I pushed my speed. Some tumbleweeds hid a pothole until it was too late, and I hit an asphalt chunk the size of a dictionary, fish-tailed due to rear weight, and slammed the bike after 5-6 wobbles. Lost a front wheel and a LOT of skin; I was bleeding for three days. I had to ride 90 miles on a severely untrued wheel to get to a train station so I could take a 3-day train home.
Not a good experience. I decided to take weight balancing seriously.
This was the "improvement" to that setup for 2014:
This rides much smoother, almost like an auto-pilot. The weight is basically the same as before, minus a few items. The capacity is slightly dropped. However, with a large sleeping bag in a drybag strapped to the front rack or a handlebar sheath, I can keep my panniers free for clothes, sundries, food, etc.
I also have a "Fully Loaded" setup with a similar 60/40 weight distribution as others have mentioned, which I said I'd use for Kelley, my girlfriend, to tour with me. This has been scrapped, since Kelley is tough enough to go "ultralight" right alongside me and she carries her own gear.
Of course, my first tour (1,500 miles, unsupported, and camping) was my best setup...
It doesn't really matter where you carry it if it's only 8 pounds. Today, I usually tour with a computer to run my website and work remotely, and all the setups listed above were for 3 season/winter conditions, so I had much more stuff... but there's a simple luxury in carrying only the bare necessities and riding an essentially unloaded bicycle.