Ok hear ye hear ye hear ye!!!!!!Do
NOT use Castrol GTX , GTX II,GTX III, GTX Magnatec in your bike
ANY BIKE if you have so much as the slightest respect for it!!!
Why I hear you ask???
These oils are fortified with a friction modifier which is NOT compatible with 'wet' type motorcycle clutches. The other issue is that these oils have so many additives they have become a very 'DIRTY' oil creating excessive sludging and coating the insides of your bike engine and gearbox with thick brown varnish even when regularly serviced !!
Anyone who tells you different obviously hasn't pulled too many engines apart!
You are correct in that this subject has been raised many,many times but hey , better to ask and be sure than stuff it up!!
If you are on a tight budget , get the Silkolene semi syn from Stupid Cheap [Super Cheap auto's] ..
Note;
Your ZX6 has a pretty hard running motor and will probably be starting to burn a bit of oil by now (common).
The worst thing you could do is put shit oil in it.
Crap oil + engine wear = sludge / varnish build up = coked up ring grooves = glazed bores = more oil burning = less power = more inlet valve coking = less power.
Also restricted / blocked oil galleries ie cam etc = catastrophic engine failure = YOU DEAD MID CORNER [ worst case scenario ]
I keep the motto "oil's cheaper than engines"...think about it.
Recommended(good honest not too expensive oils);
Silkolene Super-4 10W-40 [semi syn]
Motul 5100 or 7100
Shell Advance 4T
LAST WORD: If ya think I'm being a touch dramatic and you feel you can't afford proper motorcyle oil for your mighty ZX6.... You don't deserve her!!
A Hardley would be more your ride!!!