If I go up 300 rpm how much speed do you guys think 300rpm is worth in mph say from 4800 to 5100 the boat is non step and runs 70 on gps 25p mirage plus

All Depends Where You Get The 300rpm From. I Had Props Labbed Added 2-3 Hundred Rpm And Lost Speed. It Could Happen Like That. A Lab Job Could Also Give You Rpm And Speed . Could Go Either Way. If Your Just Adding Power And Getting 300 More Rpm Then About 3-4 Mph. Full Bottom Boats Need Bow Lift. Ever Try Spinning The Props In Instead Of Out. It Will Give You More Bowlift With Less Trim. Brett When At Mercury Did A Set For Me And I Was Very Happy. It Was For A Straight Bottom 28 And Twinn Pumped Up 454,s. Props Where Cut To Spin In. They where 25 mirage plus props. This Thing Would Carry The Nose Like A Hydrostream.