I have tried both the 300 and 400 cams on my 2006 Euro 990. The 300 does take the majority of the small throttle opening sensitivity away and the 400 improves it further. Obviously the sensitivity reduction is at the expense of throttle action. i.e. you have to give the throttle more of a twist to achieve the expected acceleration. At small to no throttle openings I still find that the it is sensitive to bumps and I can sense the surging at constant throttle.
When I fitted the throttle tube (with KTM heated grips) I found that the throttle tube was fairly loose around the bar. I then wrapped the bar with a single layer if insulating tape to try to remove some of the play. This worked fine for about 6 months until last week. The tape finally slipped, wrinkled up and took all of the slack out of the throttle, inducing positive friction. This made if VERY difficult to twist the throttle in either direction. It was so bad that my hand/wrist cramped half way through a 7 hour 2 up ride. On removing the tape the problem was solved but I did notice that the throttle response was far lighter. So much so that now find it difficult to ride smoothly.
The upshot is that I found that lightly wrapping the bar (under the throttle tube) provides just enough friction to further help smooth out the throttle action. All I have to do now is to find a thin tape (or heat shrink) that will provide the required level of friction without slipping and locking the throttle. Any suggestions would be welcome.