I used to use it exclusively. Worked fine. Decided to switch to a synthetic without friction modifiers a while back, but I wouldn't hesitate to use the Castrol GTX........ and I'm not a big believer in motorcycle oils vs. automotive oils.
If there are friction modifiers the clutch will slip (unless you never use more than 3,000rpm?)
The clutch will slip with non- friction modifier oil as well, Honda designed it that way
My 550 came with it from new and needed new ring after 3 months
I've used it for years both in 10/40 and 20W50 selections and my rings are fine. While likely not the best oil it does the trick. Odd that it only needed one ring and you associate that with the lubricant. Even lesser oil will not destroy a ring in three months unless you circumnavigated the planet? 
rt
Was full set, not just one, I missed the 'S' on the end of ring (s)
Valve seals were also worn
It was re-built under warranty
I just don't like GTX, there were better oils for bikes that got ridden hard even back in 70's
I always rode gentle for first 3 miles to make sure engine was up to temp (under 2 k first half mile, under 4k for the rest)
Never believed in letting engine idle for extended periods to 'warm up'
