I would say the first option would prob work best for an adult. I have a Blood set up in a temperary tub(still waiting on the custom cages to get to me) that is 43x19.5x6.7 and it is working fine. She is alittle over 4 ft and pretty heavy bodied. I have a nice thick layer of mulch on one side and just a newspaper tent on the other and she is fat and happy.
The rule of thumb is have a snake in a cage that is 2/3 of the snakes length in length and 1/3 the snakes length in width(at least).
Are you going to be getting adults? Starting out with those will be way to large for any of the listed snakes as babies.
Also how are you going to have different hotspots in a rack? Are you having them install a seperate flexwatt strip on each level? The way racks are usually built the flexwatt runs through the entire rack and is supplied with the same power so it has the same hotspot on every level. Now the ambient temp will very by level from the lowest to the highest but its usually not much.