dvanacker,
between the two, xm 10k no doubt, and will last longer and hit harder, better growth and the color is ok by itself
but if it were me, I would do a Iwasaki 65k, based on
1. will be cheaper
2. will last longer
3. will give best growth
color won't be the greatest, but would do opposite cycle than main tank, that means the tank will be lighted only those hours that no one will be looking at the tank, and while the main tank is lighted the frag tank won't be a distraction,
but between xm and iwasaki you can't go wrong, Reeflux getting good reviews might look into it,
good luck,
sam