In June I put Mobil 1 in my '01 ZX-6R. It was the first oil change since I bought the bike in April, and I have no idea what was used before. Since the change I was sure I was getting some clutch slip over 10k rpm -- it just didn't feel right to me. It seemed as though the rpm was increasing out of proportion to the speed of the bike. Since I don't cane it all that much I figured I'd live with it for a while and change the oil later.
The last couple weeks it has gotten worse. A few days ago I opened it up and I could feel it slip-grab-slip-grab. I decided it was time to change the oil, especially since I'd like to go to the street legals at Mission.
On Sunday I replaced the oil with Motul (the dino stuff - not the 5100). What a difference! I couldn't believe I've been living with the slippage for so long. It feels like a whole new bike over 10k rpm. I went WFO in 1st this morning and I swear I lofted the front end by a couple inches. I'm kicking myself for not biting the bullet and changing the oil earlier.
Moral? Well, I'm planning to stick with motorcycle oil for my baby from now on.