FWIW, we run 25-30 yph on a 30" wide sluice (2x15" split), running expanded grating over moss. ~40" header/slickplate /damper, then 10' long sluices with boil boxes (not in avatar photo) at 1/3 & 2/3 intervals down sluice. I feel it works well.
If you wish to reuse your water a dewatering contractor grade Honda will not last long. Then you are into industrial grade like Wacker Neuson
Wacker Neuson PTS4 V, 4" Centrifugal Trash Pump, 0620971 ( 16hp - 705 usgpm) rated solids 2"
I use this pump and it was well worth the investment.
United Rentals had a 2012 model on the island for 1800$ and let me use a loaner newer 2015 model to try out to see if it worked for me. It was perfect for all the clay we need to wash. I pulled the trigger on buying the older one and had it sent up, but it didnt run as well as the newer one I tried, same motor, same pump body, same everything, and the shaft seal leaked. I called them and they stand behind selling quality used items. Their mechanic tuned the motor up to spec, replaced the seal and even replaced the impeller. He had some sort of gauge to measure the suction and brought the old one back up to the newer ones specs. Works great.
Pretty good deal, that's cheaper and way better performance than a caged 4" Honda pump. Hard on fuel though. Gotta watch the run time carefully. Needs a bigger tank.