Sump flow rate

[ruslicus]

I am setting up new a system. 65g DT with 25-30gal sump. I am using RLSS DC 5000 return pump at 4th speed which is about 1000gph a level zero. My return is about 1,5m high which makes 500gph at return point in DT is it enough for sump filtration or it is too slow? When I hold my hand in front of return nozzle I feel the flow but not crazy as I used to see. Is there any rule of thumb on flow rate in sump? Thank you