There must be something definitive out there.
I know from personal experience that once a room gets to 80 degrees Farenheit, many computers will begin to experience problems. In my first computer job in 85, we had many days off because the mini computer was not in a properly cooled room. We actually set up a thermometer and shut the server down when it got that hot to avoid crashing the system with many users on it.
But you have to think about it from a weakest link in the chain perspective.
Computers generate large amounts of heat - especially processors and hard disks. The cooler the server room is, the easier it is to keep these systems running at their optimal temperature.
To avoid any failures you have to keep the room cool enough to avoid failures on your hottest box.
Our data centres run at 68 degrees.
James