Should have added that. This is the setup,
I have plumbed my 600 with dual Laguna 4280s.I will have 5' of vertical head (3300gph). I will have to run 1" clear tubing from each pump up to a 1" ball valve. From there I will have to reduce down to a 3/4 Y and split up to two different bulkheads from each pump. (4 in total return bulkheads). Appx 3' of 1" then 3/4" Y and 3/4" rest of way through bulkheads and up to outlets. (Appx 3' of 3/4" plumbing)
So my question is how much will the reduction in plumbing size from 1" down to 3/4" effect my gph. Just wanting to have an idea of how much of a decrease it will have. Not sure there is a exact number.