How much do you intend to carry? I would tend to agree with the local shop's assessment if you're really looking to go fully loaded. I think the wheelbase is just a little too short and the head tube is a little too steep to carry more than about 50 lbs. On the other hand, as an ultralight backpacker, I don't need to carry more than 35 lbs. for two consecutive nights in campgrounds with running water.

I stand just a hair under 5'7" with short legs and ride a 48cm Double Cross built up at just under 23 lbs. without the rack, pedals, cages, etc. I find the bike is rock solid stable with the typical 20 lb. commuting loads. The lightweight rack starts to get scary wobbley at 30 lbs. which is above it's rated capacity. If I mount the heavier duty rack on there, I swear I can feel the rear wheel flexing at about 40 lbs. It's a 32-hole Open Pro laced to an Ultegra hub and it didn't stay true for long with me going up and down curbs with multiple bags of groceries.

I figure if I had a 32/36-spoke wheelset with tougher rims I could carry another 10 lbs. or so before the geometry as well as frame itself started to get hard to handle. I'll bet I could get by but would just as soon have another bike dedicated to such duty. My Aurora has 36-spoke Bontrager Mavericks, a 20mm longer wheelbase, and is noticeably easier to handle with a good load of groceries. Unlike the Double Cross though, it feels like a bit of a tank without a load. Losing that extra mph also makes it much tougher to hang in with roadies.