yeah i'm with hammy, no way to really tell. if you want a benchmark to shoot for though. 1 gram per watt is a great place to start. and if this is your first time growing pot. don't get too upset if you don't even come close.
In a 4x4 with 2 600w I was getting on average 20oz using scrog with a couple different strains. With a 5x5 space and 2 600w I was getting on average 26oz, but was improving with each grow depending on the strain. Being a first time grow, If you get it right, you will probably pull a good 10-16oz, but then as you learn the strain and get your methods down, and begin to really dial in your space, you will see continued improvement in yield and quality. PM me if you would like any personal help with dialing it in, or post your methods here for open help and opinions Plenty of top quality growers here willing to help