Jake,
The four-blades are generally used for high-speed running, like for a bass-boat. At least that's my understanding.
You didn't mention and I can't remember if you have tabs and/or a permatrim. Both will let you nose down at slow speed and punch thru chop while staying on plane. The combo works fantastic.
When we first got the boat I did a ton of research on props trying to find some better perfornamace for not. Talked to them guys, Andy at SIM, and studied all the forums. Andy even sent me a Reliance SS to try out but it wasn't enough better to warrant the $600 investment.
Fit the largest diameter wheel that will fit under the plate - that will give you the most bite in all water conditions. Then fit the pitch that will give you peak rpm for your motor rating - in my case it's as close to 6Krpm as possible.
I'm not sure how the guy arrived at the 15.25x15 he put on mine, but it works exceedingly well. Good hole-shot even for the wimpy 150, and good performance on top. The bigger prop is good for ocean chop. Top speed is a mile or two under the factory performance stats due to the smaller pitch. The few SS props I tried gave me a mile or two cruise and top speed, but the extra weight made the lower unit chatter at idle when in gear. Was very annoying. In the end I just ended up going back to the stock style 15.25X15 and thru the original in a bag in the bow storage.
So I can't tell you exactly which prop to put on there, but hopefully that will help you select. You may not get any better than what you've got on there. But if a 15 would fit, then I would be looking for a 15.25x17 or a 15.5 if it will fit. It should pull a 17 pitch no problem. The yamaha black steels are a really good prop at a good price point.
Personally I like the aluminums, but then I don't hit stuff or run aground. They are cheap and I carry a spare. I like that if you do hit something it breaks the prop instead of the gears. A lot of guys like the look of SS, just for the shine. You should also look at the SWSII props, but I think they designed those for the new bigger four-strokes.
