Doc, I hate to tell you this, but in my experience with testing various brands, both synthetic and non-synthetic, NO 10-40 oil, much less a 5-40, will make it to 4000 without shearing down to what you see on your test.
In order to hold the viscosity to a reasonable level at 4000 miles, it takes a quart of 20-50 added when the oil is changed. This may be a bit contrary to BRP instructions, but the vast majority of big bikes on the road call for 20-50, so I began adding a quart back when I had my '11. I am now doing the same with the 1330.
My current fill is Motul 7100, a pure ester synthetic, not the highly processed dino that many U.S. companies are allowed to call "synthetic". I have another 1200 miles to go before reaching 4K on the Motul and will then test it.
Unless it turns out to be the miracle oil, which I highly doubt, I plan on using a good quality synthetic like Amsoil and changing it every 4000 and the filter every other time. This seems the most reasonable way to go for me. For this coming winter I will leave off the 20-50 and go full 10-40 as it doesn't get all that frigid here in the NC. If the mood strikes me, I may put in Rotella T6, a 5-40 synthetic, rated
Jaso MA (or is it now MA2), knowing it will get changed at 3000 or shortly thereafter.
Generally speaking, the wider the range, the faster the viscosity shears down, and 5-40 has not held up as long in big bore bikes as a 10-40 or heavier oil. Nevertheless, its a decent oil, inexpensive, readily avail at Walmart. Seems to me like a good winter oil, suitable for the short haul.
