I have heard of people setting it that high but I never had any good results with timing over 2mm BTC. I always set it at 1.8 with Tomos even with the Parmakit CDI. If your riding around town you won’t get into the upper RPMs where it will retard enough to cool it off.
I wouldn’t experiment anymore until you got a temp gauge. In the end you want a good ratio of power with temps below 400*f