Concerning the LEDs: I would consider offering the Nichia 219C (Datasheets: cool-white and warm-white). It is the third generation "219" LED with an even higher efficiency. It has the same footprint as as older 219s and all the Cree XP-LEDs. It is available with and without high-cri (the 90CRI version will be available soon). Is has a much, much lower Vf compared to the XP-G2. In terms of lumens/watt the 5700K 70CRI version is more efficient than the cw XP-G2 S4.
The new XP-G3 is more efficient than all of them, but it has a lot of problems. When using reflectors the tint is not uniform across the beam (blueish spot, yellow spill).