The way you're examining the thermal performance, your comparisons, and your interpretation of your own data leaves
barrel-lots to be desired.
A general point: You never discuss the # of fans used in each case, or the speeds at which they are spinning. How can you possibly make fair thermal comparisons without trying to keep either airflow or noise (one or the other) consistent for each case? Or at least make information about fans and speeds available to the reader.
1) One assumes, one hopes, that you installed and used the same system in each case but because you never say this, the question has to be asked. Did you?
2) Why report some temperature vaguely "near" the CPU when the CPU core temperature is available from the mb? The former is complely dependent on specifics of airflow in each case; the latter is incontrovertible. This is a no-brainer.
3) Ditto the temps of the install HDDs -- why not get the readings directly off the HDD thermal sensors?
4) The significance of the differences in the PSU exhaust temperatures is so blithely misunderstood it's astonishing. It shiould be obvious that the P180 PSU exhaust has the lowest temp because none of the system's heat except the HDDs is being ported through it. What's not as obvious is that
this is a key reason for its lower noise -- under load. When the system is worked hard, more power is delivered to the components, which = more heat. In the other systems, a lot of this heat has to exhaust through the PSU, which makes the thermally controlled fan in the PSU speed up to compensate. In the P180, this occurs at a far higher power load level, because it doesn't have to deal with the system's heat. While the same PSU in the other cases are getting louder, in the P180 the PSU remains much quieter.
Did you pay any attention during testing? Did you listen?
5) There are 4 drive bays in the lower chamber HDD cage, and this is meant to be the main HDD cage. They are cooled by the PSU's own fan.
BTW, in the latest P180s, Antec supplies adapter clips to turn the upper HDD cage into an intake fan duct for a 120mm fan to cool graphics cards. The latest versions also come with ventilated PCI slot covers which, in combination with the front mounted 120mm fan, can help exhaust the heat of the VGA in a straight line out the back. This is far better than the separate VGA duct system, which was never a useful feature, and which is no longer being supplied with the case.