You are not going to like using XP-L2s.
They have quite poor color quality, and large tint shift. It can be easily seen when the light is diffused and turned into a green beam.
IMO, I would recommend the LH351D for absolute maximum efficiency with great color rendering.
LH351D 4000k: https://www.digikey.com/product-detail/en/samsung-semiconductor-inc/SPHWHTL3DA0GF4TPQ6/1510-2333-1-ND/8568349
LH351D 2700k: https://www.digikey.com/product-detail/en/samsung-semiconductor-inc/SPHWHTL3DA0GF4VPN6/1510-2328-1-ND/8568344
Tint mixing is extremely nice, and will make for a very nice beam. It’s still quite efficient too 
For a driver, I would just go with a buck boost converter. Make it simple 
HOWEVER, I would just wait for the BLF lantern:
You could buy one and put extensions so it can run for much longer periods of times.