I run my tank right around 80 at the moment and everything seem to be going well.
I use traceable thermometers as well to calibrate everything. We use these in our lab on a daily basis so we have about 6 boxes of these things on hand at all times because some people tend to spill some nasty stuff on the plastic. These are the 0.2 degree accurate thermometers from Fisher Scientific. The cost we get them at works out to be quite a bit less when you buy 10 boxes.
Fisher Scientific Traceable Thermometer
