At that room height you'd just train your plants to keep them short and scrog, I've seen people run plants within couple feet of regular 1000w lights, not sure how much different the de ones are. If you absolutely have to keep them 4' from the canopy that'd be tough.
Have you considered LEDs? I always have to ask people when they're doing a bigger setup that I assume is for profit because good LEDs pay for themselves if you can swing the upfront cost. Depending on your electrical costs and how often you change bulbs, and how expensive those bulbs are, you can usually recoup your money on a commercial grade LED within 2-4 years. That's before considering the savings by using less AC equipment and electricity, or the increased yield due to better light spread and the fact that most of the 4x4 commercial fixtures are closer to 1200w de replacements (consuming 650w-700w).
To run through a hypothetical I'll compare a $250 1000w de
Gavita to a $1300 645w Fluence Spydr 2p running a 12hr flower cycle, I'll assume a $0.13/kwh electric rate. The Fluence uses $367 per year in electricity, the
Gavita costs $569 per year to run, a difference of $202 per year, adding in a bulb change at $80 that brings you to $282 per year in extra costs with the
Gavita. That brings your break even point to just over 44 months just factoring the light's electricity and bulb replacements. That's trying to be optimistic about the
Gavita, assuming a low fixture price and a fairly cheap bulb replacement only once a year. And if used for 18-20hr veg cycles you see a return quite a bit sooner.