For a 75gal tank,700gph after head loss is a good flow rate through your sump IMO.The QuietOne4000 does 650ish after 4 vertical feet of head,3 elbows,2-45's,and 1" PVC.BTW,I use the QO4000 on my 75 too
I like it,its got a small profile compared to the competitors equally rated pumps.Its quiet but not silent.The main thing i like about them is the 1" intake/output.