VHO's? what size tank are you running them on? you should do one 10,000K and one actinic. if you're setting up 2 48" VHO's over a 55 you should be ok for some lower light corals, but why not 4 48" bulbs instead?
On a 90 display 2x110 VHO's would be rather low on the lighting scale. What corals are you considering? The lighting choice will be in large part determined by your coral selections...but I'd suggest either 4x110 VHO's for lower light corals and possibly a combination of MH's & VHO's for higher light corals.