The temperature of the core is pulled from MSI Afterburner with the max reading used after a completed run off 3DMark Vantage and the Performance preset.
When it comes to heat, the R9 290X 4GB is a warm running video card with 94c being seen at load. This is set under the Catalyst Control Center, though. If you're not happy with this number, you can head in and lower it, of course it's going to come at the cost of noise levels.
As for the difference between Quiet and Uber mode, the temperature was the same.