Very interesting things in this thread. Looks like using bare emitters over stars is not better like the luxeon days when it comes to epoxy, since the stars on most SMT LEDs can be soldered to the star instead of thermal adhesive. Even the substrate of the star is better than epoxy right to the heatsink for heat transfer it seems.
Also, the 4500k LEDs probably use a warm white phosphor, which those are typically more fragile to heat, so the diming on those is probably due to the phosphor heating up and loosing efficiency.
Over driving a large die that is already at a high wattage is going to get tricky compared to a smaller die (like the XR-E) that is in rough the same size package. If the SST-50 was in a larger package, then it might bet easier to over drive it.
Looks like soldering it directly to a copper heat spreader, then fixing that to a large aluminum heatsink would be the best. I'm still wating for someone to come up with a copper tower that we can solder the LEDs to, then attach that to whatever flat heatsink in the mag tube that we want to continue the thermal path. That would rock. It would just need to be a tower with a flat/round base with 2 holes for screws. Then you could put your aluminum slug however deep you want in the mag for focus (mag rebel LED,etc) screw down the copper post and you're done.
