LightingQuestion

[myinfo]

Hi:

I am new to this hobby. This may be a dumb question, under what scenerio you need a 400w MH. I currently have 1 90G with 4X48" VHO. I am thinking of upgrading it to MH. Should I use 2x250 or 2x400?
Currently I have no SPS. I plan to keep some SPS and claims after the upgrade.

I currently have 150 PD live rock, CC sand bed, the tank is 48 * 24 * 18.

Thanks