if you want a little more rpm you will probably need to put a little more blocker in your intake loader and take a little bit of water away from the pump that might help the motor rpm.
Blockers can affect lots of things, or they can add lift for the rear of the boat. Each boat is affected very differently. For instance at bakersfield, I tried a slight blocker on one pass and it cavitated out of the hole unlike the loader before with no blocker and actually pushed the nose down slightly and I lost 4 mph on the top end, and it had zero affect on rpm.
I personally wouldnt run a blocker to increase rpm, I would cut the impeller down. If you do see a gain in rpm with a blocker, I would think that the pump is running ineffeciently thus creating cavitation which it not a good thing. just my two cents.