1) Whats the consensus on using the XP-G or XM-L Crees?
2) I was planning on using the Mean Well ELN-60-27D, however it seems this particular driver is sold out or not in stock pretty much anywhere... Any alternatives?
3) Is there any way to use the same power supply for the Crees and also for moonlighting?
1) XML for planted tanks works great. You have the option of switching out the driver long term if you want to produce more light
XP-G is a cheaper alternative but still produce amazing light
2) Meanwell arent "sold out" they are going the way of the doodo bird (sp?) They are old technolgoy and really arent designed for the LEDs you see out by CREE. You should look at Inventroincs http://www.ledgroupbuy.com/constant-current-drivers/
Extremly high quality, dust proof, water proff (IP66 and IP67)
With the meanwells you mentioned, you have to actually open them up, tweak the internal settings so you dont blow the LEDs when you first plug it in. Sometime they come at 1.7A which will mess up any XP or XT LED and even XPG
3) Not really. Best way to do moonlighting is to get a separate moon lighting LEDs/power supply or get a controller like the DIM4
that can control your display lights and run moonlights without any extra power supply/drivers