Yeh Xt-e are nice too, i believe XMl has a wider spectrum all around. You can get the Xm-l for $6.50 a piece, ledgroupbuy.com I run the xml's around 1800-2000ma, which is recommended by cree, but it can go up to 3000ma depending on cooling, but not much or a difference in lumen output. So i would say 2000ma is best, which is around 742lm a chip. You would need two Xt-e running at 1500ma to match that highest bin 856lm(full blast).
also Xm-l's run at a average Forward voltages of 3.4, So the only down side is you would need twice as many drivers or (driver voltage) and watts for the 2 XT-e's(3.4v x2 =6.8v) to match 1 Xm-l. Dependent on what you prefer. They are both really good chips. Just glad we can share info here, DIY is the way of the future...for sure