skipm said::welcome to nanotank!
I would use apair of 250 watt HQI DE MHs, the studies that have been done by Sanjay Joshi comparing the 250 HQIs with 400 watt MHs have shown that the 250 have a higher PAR value. Since you will be using 250 watt bulbs it will cost less to light the tank. HTH, Skip
PS I would still supplement this with VHO actinics.