another ic retro or 2 250w mh?

[1mbrews8]

right now, i have a ic660 going to 4 48" staggered t5s. it's in a canopy over my 150g. i want to do more sps, etc. should i go with another ic retro setup (would be 8 48"t5 staggered. or get a dual ballast pushing 2 250w mh? thanks and please tell why...
mike

 

[johnr2604]

What are your tank dimensions?

 

[1mbrews8]

its 6' by like 20 by like 18? i'm at work now. 20-22" tall i know...