Stacking-optimization is one of the reasons I will never trade in my first-generation Scion xB. It dwarfs the cargo capacity to engine size (or MPG) ratio of anything else you could buy. I usually go over the cargo weight capacity before I run out of room.
I will keep rebuilding the engine on this thing until batteries become better, then I will put a 200kW motor the size of a grapefruit on it with a 100kWh battery or something. I love this car. Too bad they screwed it in 2008. The new Cube is ok, but the xB1 is still better.