Just for a reference... I can attest to a fully loaded Passion (comfort, PS, Sound system, etc) doing fine with higher than rated load, at least short term. I drove 10 miles round trip with almost 650 pounds of passenger load, returning to base with another 20 pounds of groceries. I never felt like the Smart had any trouble. Neither did the SUVs we overtook on the starting line. Suspension was normal, over bumps and those small hill-bumps that launch a larger car into orbit. Engine never groaned or lugged as I've seen in another ultralight car.
I don't know what it would do over 1,000 miles, but 10 was fine.