Wally, I love the set-up you've got there, especially up front.
I wish I was a little bit taller...
Minh, I've owned a QB for 5 or 6 years. I recently traded my Orange 54 for a better-fitting, but less-fast ;) Silver 56.
The 54 always had a front basket on a small Campee rack. I camped and erranded a lot on this bike, plenty of long rides in-between - it was my only bike for some time. I never experienced wobble nor shimmy, and really pushed the limits on load weight - in fact, the fork crown stay of the rack broke (not at the weld, mind you) on a mostly off-road 2-nighter around the Santa Cruz Mountains in CA, catastrophe gratefully/luckily avoided. It was fixed by listmember David Parsons. Since then, I've been much more careful with how much weight I add on that rack. Anyway, steering generally always felt totally great.
The 56 is more of a French fit, and it currently holds a Swift rando bag. It's fendered, and its main purpose is a wet-conditions SS road/rando bike. I have a commuter now that does the errand haul with a sturdier rack, so the QB's load stays light; only gets what I need for a day's ride. I'm currently in the middle of a bike-parts-switch-up, and it may end up getting moustache bars (I was recently surprised to learn I love them), and an Erlen rack + small Fabio out back. I've never ridden with rear weight on the QB, and would like to try it out, as others have recommended. I have tried rear weight on various other bikes, most recently a '92 XO-1, and have never liked the feel.
The other main thing to consider with a large handlebar bag, besides your bar width as Joe pointed out, is how high your bars are in relation to you front wheel, and how/if the bag is supported. Yours looks fine in the photo, but something to consider. Once a week or so I try to commute 33 miles each way to work on the XO-1. I use the small Fabio's, supported by a homemade "Pec-Dec". It holds just my laptop, charger, clothes, snacks, journal, few toiletries, other small incidentals (read: junk). It could fit more, and even with weight, the bag feels sturdy, the steering different but comfortable, smooth, responsive. But the bag, even with the support, just barely clears enough when stuffed with stuff. I need longer struts.
Anyway, hope that's all helpful.
Patch
NYC