Might as well just use 8.
Edit:
I didn't realize you meant an actual strip inbetween the fixtures. I thought you were saying a single board there as to even out the gap, implying use of seven total, so I figured might as well just use 8. But I still don't really understand why you'd want to have only 450w(3@150) per 4X4 instead of using 4 boards and hitting 600 watts on each side of the tent?
Go for it if its the wattage you want. I base my lights on 1m x 1.2m cannopies (like a 3.3 x 4) so 450ish seems fine for that.
Also not sure how to fit 4 boards in there while mainting a little room around the boards. If you put these boards wall to wall you will get a slight hotspot in the middle. Having some space around them, around 5-6 inches helps to mitigate this. Or you can put middle boards on separate drivers.
But i dont really think you need the full 600w with this type of fixture. Its more important to try to get some board over most of the cannopy, to design it in such way so that you can dial in your ppfd by raising and lowering the fixture. Follow this:
Max 150w per board
Max 5-6 inches between boards
Min hanging height 5-6 inches
Cover the cannopy until the edges in boards
And you will have plenty of light just lowering it a bit. When you have them on hand youll see it easier: its not so much about watts per square foot its more about form factor and even cover, making sure the cannopy is covered all the way out to the sides with board, but leaving a little space between board and board.
2x 4 boards wide on a hlg600 would be absolutely perfect for a 5x7, due to the form factor. If you can work out a way to get them.into a 4-8 evenly distributed 600w should be fine. Its just more about how you space them than wattage.
And if youre getting 2 packages, get the 12 boards. They are incredibly useful in vegg and cloning aswell. OR sell fixture to a mate with the spare boards. Theyre just the easiest thing to work with as long as it fits your dimensions.
I fully encourage you to try anything.
