That's a sinking feeling. I know that feeling when a bag starts to fall and in the time it takes to hit the ground you realize you aren't fast enough to stop it, you wonder when the last time you backed up your data was, and you wonder how much a replacement will cost...all in the half a second it takes to fall.

I think a pannier falling is just as likely as a backpack strap breaking though. And for what it's worth a pannier sits maybe 12 inches off the ground where a backpack is 3 or 4 feet off the ground (depending on the size of the rider and bike). So I'm much happier with my 13 inch laptop in a pannier.

The ONLY reason I suggest a backpack is that a 17 inch laptop is just big. And if it's snug in a pannier, it's putting pressure on the fabric and seems of the pannier. A 17 inch laptop has mass and weight. As the bike bounces the laptop will exert force on the bag that will eventually cause it to tear. Probably not catastrophically where the bag rips open and everything goes flying. Bit if the bag it packs tight with a hard object, I think the bag is prone to tearing over time.

So I stay with my original opinion. Backpack that's plenty big enough or smaller laptop.

Heel strike is one thing I could spend design time on - what you see there is narrow enough in front that I didn't have any ... except when my heel turned in and I'd feel a nudge on it. The whole thing is pretty narrow, and I could cut more off since it's a tri-fold, but unless it becomes annoying I'm going to leave it as is.

I'm not as convinced that it has less shock in a bag on your back than tight in a pannier. My back will take up some shocks, but there could also be higher amplitude bounces generating bigger impulses. It makes me want to use a couple of accelerometers and compare.

I use an Ortlieb Office Bag with the QL3 mount. I have to carry two laptops: a 15" Dell Latitude E6440 and a 15" Samsung ultrabook. The 15" Dell fits fine inside of a neoprene sleeve. A 17" might fit without the sleeve.

Pannier for everything.

Backpack for nothing, on a bike.