It works well with a lineloc system. I am running the sicce syncra 5 (1321 gph) on my 120 (2 overflows) with no problem. I personally would rather have too much pump than not enough depending on how your plumbing is set up you might want to look at the 6000. with the 4000 you are only looking at 650 gph at a 5 foot head height. plus every 90 your plumbing has is the same as another foot of head height. one tee and one elbow you will be looking at about 500 gph with the 4000 and 800 gph with the 6000. 2 overflows with 1" drains will flow about 1200 gph (600 per).