Yeah, at even 8V without any sag it will heat up quite a bit. If you can adjust that BEC down so that VIN is closer to VOUT your efficiency will improve greatly.
The XHP50.2 is a huge win!!! Put it in a Convoy C8 using the smooth reflector without any modifications and the beam is pretty good---actually very usable. FINALLY an XHP50 that works good in smooth reflectors! Extra motivation to get that boost driver into production. 
