With that 4 blade you might be able to lift the engine on the transom and it still bite (depending on the prop, hull, etc). The 4th blade generally will pull a MPH or so out of it, the extra blade has a little drag. I think if you could lift it a little and play around with the setup, you should see 30 with a light load. The more you load it the more it's gonna slow down, and that's a big hull already for 25hp. The 40 outta run 30 probably not much more though-remember-it's heavier which offsets some of the extra power. Have you considered a jack plate, PT&T or breakaway? Those would lift it and move it back and in the case of the PT&T (CMC is popular brand), you get that extra benefit of power tilt/trim. Most that install them see 2-5 mph improvement after playing with it. I want one; can't justify the cost right now with everything else going on.