I've been using Valvoline MC oil since 2004, about 20000 miles. I'm a bargain shopper and finding JASO oil at the bigbox store on sale is fine by me. I've seen it at AutoZone and Advance Auto as well.
My experience:
My clutch is not in the best shape, good for normal riding, but just gives up when thrashed. It was much better for quite a while after I deglazed the plates, added Barnett springs, drilled the extra basket holes. I have new friction plates on hand, but I'd rather ride the bike than work on it.
Finding neutral when stopped can be a chore, but this K1 has never been a slick shifter like my K0 was.
Leaks: top end is pretty dry since 2008 rebuild, bottom end maybe a small seep here or there.
I haven't tried a bunch of other stuff to compare.
I've seen Terry's condemnation of Valvoline oil, I'm not doubting him one little bitty bit, but its not my experience.
I saw bwaller's Blackstone labs thread recently. It'd be nice to have a library full of used oil test results, a running history on my bike, and the smarts to understand it all. I might do an end-of-season sample and post results.
From the Valvoline PDF's: 0.112% zinc for MC oil, 0.083% zinc for conventional automotive oil. Thats more zinc, but not a whole lot more.
VR1 racing (non-JASO) 0.14% zinc