I'm deciding between getting an AP 12 shelf CB70 rack or 4 RBI 3 shelf CB70 racks. The Animal Plastics unit is the cheaper option, but I'm a bit concerned about consistent temps in a rack over 6ft high. If I go with the smaller RBI racks I will stack them and use a Herpstat4 to give finer control over temps. I'm just trying to determine if this is really necessary.

For those of you with tall racks run off a single thermostat, what kind of temperature fluctuation are you getting top/middle/bottom?