Depends more on the amp than the speaker cabinet.
That half-stack is what I play through. The volume is always extremely low.
Of course, it helps that the walls, floor and ceiling are solid concrete
My building's pretty damn soundproof. And my neighbours haven't complained yet.
Keep the wheels on, though, as they'll help reduce the amount of bass transfered through the floor. That way you don't have to roll off your low end, and you don't shake the lamps downstairs as much.