Unfortunately, while lasers do appreciate good heatsinking, they are not like computer CPUs where if you just keep cooling them down you can overdrive them almost indefinitely.
With laser diodes, once you go past a certain current (which varies slightly from diode to diode) instant death will occur regardless of how much you cool the laser. Heat is not the sole determining factor when it comes to lifespan, nor is it the most important factor. Diode current is the most important. The more conservative your settings, the longer your laser will last.
With 6X diodes, I'd say that 200mA is the absolute maximum current that will allow you to see at least several hundred hours of operation. 150-175mA should allow for thousands of hours. Then all you need to know is what kind of system the diode will be used in (pointer or lab-style). In a pointer, you probably won't see hundreds of hours of usage in it's lifetime since time racks up so slowly on pointers, but with lab-style systems you'll most likely easily see thousands of hours usage in it's lifetime.
