[Fr. Frank]

That 1983 "115" hp motor is capable of producing over 170 hp at between 8000-9000 rpms. The inline 150 version was capable of making nearly 240 hp at 9200 rpms. But you DO NOT want to run it between 6200 and 6900 rpms, unless you're rapidly accelerating through that range. Mercury ran some tests in the early 80's and found the I6 motors will self-destruct rapidly if run continuously in that range, with the most destructive range being 6400 - 6700. Something about destructive harmonics.

For normal use, you should consider 5500 as the maximum rpm at which to run continuously, i.e.; for more than 10 minutes at a time. A few minutes at 5800-6100 will not be a problem.

You should be able to reach the max normal operating rpm (5500) with your boat at maximum gross weight. So propping your boat should be done with full fuel, and max persons on board (or their equivalent weight). That also means you will be able of exceeding that rpm with anything less than a full load, which is appropriate.

You can make the oil switch all at once, if you want, by just using the Quicksilver oil the next time you add fuel, because you're pre-mixing. The Quicksilver synthetic blend oil will mix/blend with any 2 stroke oil already in the tank. But if you've already got some OMC oil left over, use it, don't throw it away, it's good oil. Just don't use the really cheap stuff they sell at the major discount stores.