You cannot rob Peter to pay Paul……. If your slippage is .29 at cruising speed that i9n turns means that you are getting 71% current propeller efficiency. On a keeled hard chine Harris hull you and not doing to bad at all. The best way to decrease slippage is to increase diameter, however I am sure that you have already done that. Next we can increase blade area; however increasing blade area will reduce your pitch. The last thing which I am not a big fan of is to add some cup, however cupping is also not free and it may cost some drag.
Based on vessel & its current power I would not use either wheel. I would find a new Michigan
Dyna quad with max diameter, no cup & pitched to correct load with a full blueprinting to make sure every blade is working as a team.
Next I would address the shaft and make sure that your wheel is a far away from the keel as possible.
After all efforts I would est that the best efficiency you will ever get on your hull is at best 77%. Do the math and see what your increase is.
Lastly I would take a hard look at any possible weigh saving items, reduced weigh will also decrease slippage.