Some bikes. Hell, they're all the same, ain't they?
I ended up riding the long way home yesterday with my Chrome messenger bag on my fancy road bike, and I hated it. I've had a nicer time with panniers or trunk bags over longer distances.
It felt like I was going faster, and it was partly true -- this bike had a more aggressive riding position, which tucks me out of the wind more. The placebo part, though, was only because the weight wasn't on the bike, so it appeared to surge forward more responsively whenever I pedaled hard... yet the Chrome bag and its contents, I'm sure, are actually heavier overall than the same stuff in my cheap panniers.
Just because your baggage is on your back instead of on the bike doesn't mean that it magically disappears. You still have to transport it, and it will still slow you down, and it'll still make you work harder on climbs.
Road bike, road bike, road bike (folder). See a trend here?
I had a messenger bag. It was ok. Nothing special. Somewhat irritating at times. I switched to a single pannier a while back and never regretted it. Didn't notice the extra weight (clothes, lights, lunch, sometimes laptop), didn't get sweaty. The only time I actually notice it is when I am carrying the bike out of the front door in the morning, especially if I know I will be stopping on the way home and have taken a heavy lock as well.
How would you fit enough weight to affect handling into a Carradice Zip Roll bag? I've seen it - it's not a particularly large bag...
But I don't think moving your weight from a trunk bag to a seat bag (like the Carradice Zip Roll) is going to help. If anything, by putting the weight up higher it's going to make it worse.
I would think if you have that much weight, it would affect handling as well on a handlebar bag, though I have to admit I haven't tried it.
I tried looking up the "deuter rucksack", but I couldn't find a picture. It sounds like it's probably one of those bags with foam on the back and stripes making channels through the foam, right? Those don't do the best job.
The style of bag I've found that works for keeping the back dry is the kind that has a mesh that rests directly against the back, and a hard plastic shell behind it that keeps a small gap between the mesh and the actual back of the bag. I have a bag from deuter like that that works great for keeping the back dry...though it's inflexible and makes it hard to bend over on my road bike. The best bike I've seen (seen it in person, though haven't used it on the bike) is the Detours Sienna 40 - it has the same mesh/plastic backing, but it seemed a lot more flexible: http://detours.us/product_info.php?p...=125&language=
Really though, if it was me I would just put everything in the trunk bag and just get used to the handling being a little different.
I've experienced panniers slowing me down as well - I think it's the wind resistance against them. Another thought is to use a single pannier and a trunk bag. If you could cinch the pannier up flatter against the the bike, you could put the really heavy stuff in the bottom of the pannier where it would affect handling the least, then put the bulky but light stuff in the trunk bag where it wouldn't affect handling as much.
I'm currently using a small/medium hydration pack, minus the bladder (bad valve & bladder quality); it doesn't fit well, but I don't feel the weight. I carry a pump, spare tube, tools, a couple re-useable shopping bags, and my at-work necessities. I have another, larger backpack that I use in the winter.
I tried the messenger bag route, didn't care for it -- maybe I didn't have the right one, but.........
The best thing I've ever used is a small waistpack -- about half the size of a six-pack cooler, with carriers for .5-liter bottles along each side. It failed due to the low-quality snap-buckle. I WILL find another...!