No, it will rock. Not equal to gsxr 1000, per say, but definately 90mph on dirt feels similar to like 150 on the street. Its different, but that bike will pull hard. What gearing are you running? 14-49 should be good top-end with 14-47 having more and 14-45 having more than that. I run a 13-45 that is good for tight or open riding. A 14 with optional rear sprockets would be better for top-end acceleration. Or even a 15 for open smooth riding.
It runs strong to top of the gear then? Does it seem to have a powerband thats constant to the end or pulls hard then falls off on acceleration too soon? You want as constant of a pull as possible.
Retarding my timing added some r's. And there's alot of power in the main jet and needle settings. Stock is a good starting point, but too lean or too fat robs power. Main is easy to check by plug color after a wide open run.
IMO, that flywheel weight is only for tight trails mixed with tall gearing. To each his own, but adding weight to a bike anywhere is not for speed, maybe for control. They bring a pretty penny, though,and with the money, you could get some reeds or a pipe to get some easy power gains. Add power, you can pull taller and taller gearing, which equals less shifting and higher top speeds. You sound close to being there. You can change alot about how it runs, but always do one thing at a time, and if it doesn't work, don't be afraid to go back to original setting and try something else. Which is why its a good reason to keep notes.