2.2a - 2.3a is about as hard as you want to push an 03 ......yea you can hit 1300mw @ about 2.3 but that's close to the fold back......although every diode can be a little different and there are some freaks that are more efficient.
I haven't seen any info on how much life a diode like this has when pushed hard, or operated at or a certain amount below the drive current knee. Is there a rule of thumb regarding how much below the knee, as a percentage of full current, these should be run at? Perhaps different for each model.
I doubt there's any way to know without testing but I have run nubm44's for many hours at 4.5a and they hold their output for a long time, however after a hundred hours they don't output as much, losses are in the 10-25% range and if you watch the output on your LPM you will see over driven diodes can't hold their output, they trickle down slowly but back the current down to the advertised max and they hold their output rock steady, I suspect it's a heat bottle neck in the diode due to material properties, so wheres the line between stress and damage ??? The less you overdrive the longer they will last I suspect but it's also important to use the thermal compound and an adequate heat sink, I have become fond of DTR's 20mm copper modules.....are they back in stock yet ??? The 20mm copper with heat sink compound trickles down slower so heat is a factor and when I test a diode cold I often see 7700mw @ 4.5a but after 10 seconds I shut it down, wait a minute and on the 2nd test I get 7500 or 7400mw, they are always stronger from a cold start and if you chill them you can get over 8w so again heat is a factor but not the only factor, push too hard even packed in ice and LED city.
If you only want a short duty cycle pushing to the max is ok, but if you want a longer duty cycle it's better to cut it back a little and use a good heat sink with compound.
For the nugm03 I often set them @ 2.0a maybe 2.1a but no need to push any harder, you can't see the difference between 1200 and 1300mw