Whats the extra dimension?
Iv used 250W fine in 3X3X5 (5X 50W)
Got 9.5 Ounce
This past grow went up to 457W and increase space to 3X3.5X5 (4X 50W 1X 257W)
Not noticed much difference other then harder to control temps.
Your biggest issue will be light spread from a single cob. So youd have to have it quite high up to get full coverage which 4 foot height of your tent wont give you.
IMO youd be better off with 2X 200W, Then step up to another 2X 200W when your ready to flower.
Thats true watts from the wall im talking about. Not the false claimed equivelent watts most places advertise as.