Efficiency is not an independt term and defintiely it will be linked with equipment (with in the reasonable band). If the operating parameters established appropriate, it is possible to reach around 80-85% on centrifugal machines. I am not sure why you are saying 4stages in your case. Each stage...
5000HP Motor most likely needs to Synchronus motor for recip application, though speed is in the order of 900rpm. Adding such a big motor would definitely push you starting current issues unless you add significant additional generation capacity. As discussed in several responses above, unless...
If it is permanant strainer, I think for Centrifugal pumps 40Mesh is the size vendors recommed. Normally for stabilised streams in refineries permanant stariner is not needed, as no sloids are expected, unless it is from crude oils torage tank/transfer pump service.
Original selection of drive will primarily depends on availability of power source & suitability. I would say Hydraulic system is complicated, if it is for continuos duty and controls are required.