Go with the 400W if heat is not an issue. I would suggest an air cooled reflector with either a 4 or 6" inline fan.
What are you using to cool your cabinet?i too would go with the 400 over a 250 any day ... then again i run 1000 watt in a 39" L X 39" W X 79 H
i would check prices ar HTG tho either at ebay eBay Store - High Tech Garden Supply: 400 watt Grow Lights:
or their own website at
High Tech Garden Supply
i think you will find their prices to be better and they are 100% trust worthy