On my 240 I started with the XM 10k and hated the color.....Good par, but hated the color....If you play with the nipple orientation on the bulb to the socket it's a little better, but still IMHO not appealing.....The XM 20k is a nice bulb but poor par......Should have asked is your fixture DE or SE......
Here's an old, but good link to read......
http://cnidarianreef.com/G180/lamps.php