Look at the comparisons on this site to better help you choose. I went with (2) 250w MH SE XM 10k and (2) 400w MH SE XM 20k and (2) 60" 110w VHO URI on my tank. Stay away from the XM 15k, I have also tried the Geismann 14K they are not that blue to me very yellow IMO.

Rich

http://www.reeflightinginfo.arvixe.com/