Creme brulee cooking temperature
I've never used a heated mixing bowl, but I do sous vide, which I believe works on the same principle as what you're trying (namely that you can't overcook it because the cooking temp is where you want the final internal temp of the food to be).  

Anova has a pretty popular recipe for creme brulee which specifies 176ºF (80ºC) as the correct temp.  They also have an older, less popular recipe that specifies 180ºF (82ºC).  This recipe for traditional baked creme brulee says to bake until the internal temp is 170F-175F, but with residual heat I would expect it to continue cooking until somewhere between 176-180F once out of the oven and water bath.

If I were you I would set the mixing bowl temp to 176ºF (80ºC) and see how that sets up.  If the final consistency isn't quite where you like it, you can try it a little higher next time.