I talked to the guys at Traxxion Dynamics and they suggested making the next step to the 8975. If I remember correctly the 8900E was still an emulsion shock like the stock Fz1 with just spring preload and one adjustment like rebound. The emulsion shock when it gets warm can get a little wiggly/squishy under hard riding because the oil and air mix begins to get bubbles and it doesn't hold the correct pressure for rebound.
They strongly encouraged/suggested to just step up to at least the 8975 because it has the nitrogen in there that you don't have to worry about it heating and the ride deteriorating. During the testing days they went to, most riders could not tell the difference between the 8975 and the 8983 in terms of performance and there is a $200+ savings with the 8975.
Anybody would feel better on an 8900E compared to factory because it will have the correct spring weight. That alone will make a big difference.