Nice looking build!
You probably don't need a higher duty cycle or you would have done so but if you could make sure as much air as possible is exposed to as wide an area as possible for your heat sinks you would have more heat transfer to the air. If you could make some kind of ventilation to allow air to escape the battery tube, your driver would run even cooler than having it all trapped in. Regarding that beautiful smooth heat sink for the laser diode which I do admire, just having a mass of heat sink metal will "sink" heat for awhile, but won't do nearly as good a job of transferring that heat to the air and out of the heat sink unless you maximize the surface area of the sink, this means fins and lots of them exposed to the air. You probably know all of this already and didn't need a long duty cycle or to have a longer operating time but mentioning it for others who might not realize that. I see more and more laser pointers being built without heat sink fins lately. Again, if you don't need a long operating period it doesn't matter if you keep it short and let it cool down. A large mass of aluminum, as yours, will also take much longer to heat up than a small one, buying more time before you need to shut down to cool off.
Edit: I should add, regardless of my thoughts on better heat dissipation I'd love to own a beauty like that! Sometimes form is just as important and it sure is a nice build you have there & three watts is awesome! I've never seen this done before with a huge Mag Lite and it looks great.