> I'm carrying quite a lot of photography gear and I'm thinking about moving
> some of it (cca 3-4#) to the sides of my belt.
> I guess it should lower weight of my pack, move center of gravity closer to my
> body and make those items readily available. Those pouches will add some
> weight, but I would need them anyway, because those items (lens and camera
> back) need some protective padding.
Lens pouches at the belt offer unsurpassed accessibility. Unscrew the lens on your camera, reach out, grab the other lens from the pouch, put the lens that was on your camera into the pouch, screw the new lens to your camera. Very fast.
Lens pouches do provide better weight distribution. However, for heavier lens like the Canon 70-200mm 2,8 L, the belt must be rigid. Some form of plastic "exoskeleton" or stiff foam is best. If not the lens pulls out from the belt. Even more important, the pouch and belt combo must have a compression strap to cinch the lens to your hips.
I use a belt system for urban shoots all the time. I wear only the belt and ask the client where I can leave the main pack in a secure place. I do not use them on the street, however: too easy to spot myself as a photographer.
The story is different in the outdoors. You are wearing a main pack with backpacking gear. One of the problems is when you need to put the pack down to the ground... Unbuckle the belt and the lenses pull out, the whole thing turns into a mess to lower to the ground. Those expensive lenses tend to strike the ground more often. I struggle a bit to put the pack back as well.
The other problem is after a couple of days, you can get some chaffing at the hips, due to the weight and tightness of the system.
Running, scrambling over boulders and in maneuvering in tight places on steep and airy trails in the Alps is a pain as well, but if you shoot in more gentle areas, it's okay. Lens pouches are normally designed to be low on the belt. There is ample space for the elbows doing a walking sticks swing. Walking sticks are mandatory in the Alps, even for trail running.
I would suggest to look at the excellent pouches by Kinesis Gear and LowePro.
ANATOLY IVANOV PHOTOGRAPHY / DESIGN