I am not going to tell you wether to use it or not but I will tell you the following story that happen to me and you can make your own conclusions. I know I sure made mine!!
On February 1989 I was the owner of a Yamaha 600 Maxim motorcycle. The time was approaching to change the oil and I happened to have a case of Castrol GTX lying around in my garage. I was debating for some time wether to use it or not and eventually came to the conclusion that it should be OK to use it since in my opinion the bike's engine was a regular mini version of a 4 stroke engine like the one used in most cars. True, I was contemplating the fact that the bike's engine runs at higher RPMs but first of all being a very conservative rider I was rarely revving it at more that 5.000 rpm and secondly I was planning to change it again after about only 1,500 miles to make up for the high RPM use. Anyway, I did the oil change and started up the engine, everything seemed fine. Next morning I woke up and prepared to ride my bike to school. It was very cold outside approximately 35 degrees (which in Southern California is really cold). I took the bike out to the freeway and took it up to 65 mph. About one minute later I felt a serious loss of power kicking in as if I was running out of gas. I pulled aside checked the tank, it was full of gas. Got on the freeway again took it up to 65 again and I felt the same loss of power kicking in. It seemed as if the engine was getting ceased for some reason, but I kept going. The loss of power became stronger and stronger, and a few seconds later the engine slowed down and came to a complete stop. It was pretty obvious that the engine was ceased for some reason. This was verified by the fact that the starter could not turn the engine either. I waited about five minutes for the engine to cool down and the bike started up normally. Again I took it up to 65 and the engine ceased again. Pulled aside, let it cool and took off again but this time I did not take the bike above 40 mph.
Later when I returned home I passed by the local Yamaha dealer and picked up the Yamaha 10W-40 oil. Went home and drained the Castrol out completely, changed the oil filter and filled it up with the Yamaha oil. The bike has been running perfectly ever since.
A second fact happened to me 4 years ago when I changed the oil in my uncle's 1984 American Chevy 350 V8 engine to Castrol Syntec and started having serious oil leaks all over it a week after the oil change. The engine had been leak free (actually it had the very common slight oil leaks mandatory for every American engine...), for more than 10 years.
Again I am not going to tell you wether to use Castrol oil in your engine but I am describing to you what in fact happened to me. I know that everybody can interpret the above the way they want to, but as far as my engines are concerned, I have made my conclusions.