Roy,
Can't speak for material changes in the stainless, but I can tell you the difference between the Trophy Plus and the regular is cup height. On most model of Merc. props they made them in increments of 2" of pitch. 3 blades like the Tempest, Mirage, were in odd sizes 23,25,27 etc... What they did was add the plus designation to it and it ran like a size higher because of the cupping. So now they had in effect a 24,26,28. They did the same with the Trophy when creating the Trophy Plus. Even though they made more pitches available they were still covering a slot of boats with higher H.P. and higher motor heights. For example a 27 Trophy Plus will run out like most others 28 and then some. If you took a stock Trophy and a stock Trophy Plus you would see the RPM difference. So the Tempest Plus, Mirage Plus, and Trophy Plus covered more applications without creating new blade molds, dies, etc... When propping out offshore sport boats like a 25' Baja with a 496 H.O. 425 hp, the first question is what prop are you running. Most of these were shipped from the factory with Mirage props. Depending on year and power you have to know if it was a plus or not so the pitch you recommend will match with your prop accordingly.
Mercury also did the same thing with the Bravo XS props. Instead of creating a whole new line, they took the existing prop (Sterndrive) and cut the barrel, added 1" holes and boom new prop. But what some do not know is that the Bravo is ONLY made in even pitches, so when you order a 27 for example you are getting a heavy cupped 26p. Very similar to their plus designation. Smart way to keep cost down, and offer a line which they already have... Hope this helps.
TBuck
