Craig...what prop is on it now??
Save money...aluminum
Last and more performance...stainless
Only problem really with aluminum is if you hit something with it...very good chance you will lose a blade...
Stainless if you hit something you may knick it or bend it...but probably will be fixable...you probably won't lose a blade...
There are many places to get a prop...I would try to try a few out from a friend or shop if you can. Do you have a tach?? You really need to be at the upper end of your rpm range...probably 5500 or so when you have an average load...you don't want to lug it.
I agree with IBNFISHN and PanMan...you should check both...I replace my waterpump ever other year also...some older mercs you needed to replace every year. The rubber in the impellor can wear out or even get soft and not have the contact it should...get the kit..not just the impellor since its been a while. Then just replace the impellor every other year...cheap insurace as said before. Check thermostats isn't too hard...find out what the temperature of your thermostat is and get a heat gun or some heat sticks...the stick will melt or not melt at a certain temp so you can see the range your in...you can also put them in various spots and see if you have a hot spot. Alot of merc/mariners will not pee unless the termostat is open...watch the temp gun and pee stream and see when it opens. An easier way is to just remove the thermostat and put it in a pot of water...put a thermometer in the pot and start to heat it...when it hits the temp it should open you should see this happen. If not replace...if so it may be something else...could be as simple as the water pump
"But if serving the Lord seems undesirable to you, then choose for yourselves this day whom you will serve, whether the gods your ancestors served beyond the Euphrates, or the gods of the Amorites, in whose land you are living. But as for me and my household, we will serve the Lord.” Joshua 25:15