About Thea biased presets; unfortunately there is still not much available, but if you can take part to Thea forums, you can get general and scene related help there really fast. If you are not familiar to photon mapping/final gathering - reading trough global illumination tutorial in Thea manual is a good idea. Then continue reading about Thea render settings (as with biased rendering one really needs to understand hows render settings effect to get the fastest possible render time for each scene); one can easily reduce render time to fraction with somewhat optimized settings.
There is a new progressive render method Adaptive (AMC) mainly for interactive rendering, but you can also apply IR settings to scene and then use Adaptive (AMC) in darkroom rendering.
For fast IR exterior rendering with Sun and Sky as main light source you can use settings like this:
fast_AMC.png
If you have more complex light setup and/or interior scene (with many light source), then turn caustics on.
(Apply settings to darkroom with the icon on far right to "General")