Rotella T6 -> 5w40 vs 15w40?

[redbirds_imp]

I used Rotella T6 5W40 with no known side-effects or extra noise - in fact, the lump was quieter and gear shifting remarkably smoother compared to GN-4. Sub-zero winter riding also benefited being 5W and synthetic.

I would have never considered 15W40 for the CB1100, especially for cooler riding weather.

Same for me. I have used the T6 5W-40 for all my bikes for years. When new my 2013 CB1100 was reluctant to shift at times and excessively noisy, especially on hot days. First oil change I used the Honda synthetic 10W-30 and thought the problem would disappear as it broke in but problem continued. Next change was a switch to the T6 5W-40 and noise level was better and shifting stiffness disappeared. Best of all, T6 is a fraction of the cost of "motorcycle" oils. I do like the Honda oil filters as they are shown in tests to be better than most.