145 kph or 90 mph is pretty good. That's 15 kph and 10 mph faster than the 250. I doubt there are any speed limits that allow that legally.
Single thumpers always vibrate at the higher rpms. CueBaller offers good advice on the gel gloves and loose grip. I don't know about specific grips for it, but there lots of choices out there. Just find something that you think feels good to you. My 250 is stock, but I have Keryakin grips, pegs, pedals, etc. on my Harley.
If the vibration bothers you at the normal cruising speeds, and if you have more than enough acceleration in the lower gears, then you may want to consider a sprocket change to move the rpms down for less vibration at the cruise and above speeds. It could possibly move the onset of vibration to a higher speed, and reduce it some at all lower to mid speeds.
It might increase top speed, or it might lose some but that is not what you are after, as it will be vibrating even more at top end with the higher load. You just have to decide if you can give up low end performance and acceleration, and are willing to shift gears sooner, to get smoother operation in the cruising range.
I don't know how much it will help, but it may be worth a try if the vibration really bothers you.