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With respect to aluminum vs. stainless steel and the idea that the former will protect you from impacts, it is indeed an old wives tale. It was effectively, and to my mind finally, debunked a few years ago on this very forum, where a member reported two separate boats hitting a submerged post in his harbor. One had a stainless prop, and the other aluminum, and both boats destroyed their lower units - the aluminum provided no protection.

So aluminum won't save your motor, but it will cost you some fuel economy and performance - fairly subtle, but real. And aluminum will take damage from floating debris or shell flats, while stainless will shrug it off with a few scratches.

Regarding the prop choices you list, my choice, based on my experience with the F70 on my 15, is "none of the above." My short list for an F70 on a Montauk would instead be the Yamaha Painted Stainless (YPS) mentioned by Aquanutt on the first page of this thread, the copy made by Power Tech which is the SCD3 model, or possibly the Turbo Quest.

I used a Stiletto Advantage for several years, but was never really satisfied with acceleration and top end. After thinking about it for quite a while, I theorized that with the F70's power curve, I wanted a prop with less blade area to let it spin up easily through the middle RPMs to get to where it makes its power at the upper part of the RPM range. I contacted Power Tech and after some discussion, they recommended the SCD3. Subsequent research brought me to look at the Turbo Quest, which has the same characteristics as the SCD3 and YPS - smaller blade area, low rake. The Quest is specifically advertised by the manufacturer as being a good choice for the F70, so that made me think I was on the right track. The Quest is, however, more expensive than the others. I went with the SCD3 as it was a little cheaper and they let you trade in if the pitch isn't right. I am very happy with that choice.

Don't get me wrong - the Stiletto and other large blade area props are great, just not right for the F70, based on my experience. The difference when I switched to the SCD3 was like night and day, and it made the boat much more fun. Acceleration is instantaneous, and top speed improved as well. Most impressively, I can get very close to top speed without trimming out at all - something I need fairly frequently in the areas that I boat in.

Regarding pitch in the SCD3 or YPS, I would characterize Aquanutt's 17-pitch as just a bit too high, and I run a 16-pitch which is a whisker low for my 15 but might prove optimal for your Montauk.

Tim