This stuff?
 

Good stuff. JASO certified and cheap to buy. Had it in my Suzuki Vstrom, Lynda's Suzuki M-50 and my Ford Ranger. All 3 worked very nicely with the 15-40 dino. Switched to the Rotella 5-40 synthetic in the Ranger and am real impressed with lower rpm power just above idle. Nice to have a little more bottom end power in traffic and on hilly streets. The GZ will likely thank you.
Your results may vary but I highly recommend it.

Very Good Stuff!

I 've used it for years!!! :)

Very well. I will report on the happiness of the motor ex post oil change.

50 miles on the Rotella.
Motor is quieter.
Motor comes to a stop slightly faster when I hit the kill switch.
Power seems the same.
Clutch seems exactly the same. good.

Post mileage changes in a few days. I've been consistent 75 to 80 mpg.

Good oil. I use it in both my Magna 750s and just put it in the mini van this past week end. Works great for the price. I will be putting it in my ford ranger here soon.

100 miles.
Motor still quieter (just as easy to start)
Power seems the same.
Clutch has lost a tiny bit of grip. (if I flog it through the gears the clutch can't *grab* quite as solid. But it does grab)
This is a non-issue as I normally ride, well, normal and the clutch can still hold the motors power.

Perhaps there is a tiny bit of friction reducing additive compared to say Suzuki motor oil.

Still. I'm very happy with the brand and the fact I can go to walmart, even on a monday, and buy oil for my bike ;)

I tried this oil in my bike when I got it because I've been running it in my Honda Helix scooter for years and like it, but it of course is a CVT so it will use any oil.

The GZ didn't like this oil it seemed, I to experienced clutch slippage at higher RPM's when shifting gears that instantly was cured by switching back to castrol M/C 10w-40 oil so I will just stick with that I guess. Wet clutches seem more sensitive and I don't want to tear it up having it slip like that. I've used Valvoline M/C oil to, I get both at any of the local auto parts stores near me.