your yield will go up if all things are equal. Penetration down increases by approx a foot by going to the 1k.
you'll be happy.
but to blow the roof off, two 600w combined for 1200w gives you way more lumens and results with only 200w more power.
It sounds like you are looking to increase yields? If that is the goal I would double up, and add another 600, if the space is there. Either way it should be fun.