My experience with my Surly LHT has been that rear load + handlebar bag = super twitchy bike. Transferring some of that weight to a low front rack completely transformed the bike handling; the bike feels like it's on rails, it's so stable.
I have a Tubus Tara front rack, but if I were doing it over again I think that I would look at racks with a platform for a handlebar bag. I love having the handlebar bag for long rides, because it keeps my map near my face and snack food close at hand, but it also interferes with my headlight mount. I'm planning a long tour this summer, and I've really gotta get this resolved.