the SST-90 runs fine with direct drive on 4 x AA eneloops due to the voltage drop. I guess it depends on the exact Vf of the LED though. Britelumens and Der Wichtel make good heatsinks for the SST-90.
Mac's 3300L dropin should work but it's expensive. Probably need eneloops or even Elite 2000's to handle the current.
Malkoff makes good XP-G dropins too.
I'm not sure about any high powered incan bulbs on 4 cells.