yea nice grow, I just love the LSD so compact and potent
I grew a few under a 600W
if it was me with a 400W considering a upgrade I would probably look in to vertical scrog and get one more 400W/cool tube (if you have the space for it ?)
or just add a small MH to the HPS for better spectrum, but really no need to go higher then a 400W for one plant, wast of energy and only thing it might give you is a lot of heat to fight and a higher power bill
Im 110% sure a 400W grow with perfect temps will both yield and be more potent then a 600W with to high temps
another possible upgrade would be a tent more, either to run two at the same time or to do a Veg. and flowering tent
I just down scaled to a 288W LED fixture form the 600W but hope for the same yield (yearly) as I now run a T5HO set up for veg at the same time so I can harvest twice as often (power is still less then the 600W HPS set up alone)