Thank you. That was very helpful.
After I wrote my initial post it occured to me that the bottom mounted fans might not work in some of the cases that have seperate compartments for the power supply. It looks to me that in some of those the divider that seperates the power supply compartment from the CPU compartment might block the airflow to the fan. Don't know if anyone has experienced that or if I'm missing something here. I don't intend to get one of those cases, so that's purely an academic issue to me.