Looking at the original post, is this actually a clutch issue?
Overtaking something in the motorway (I'm assuming 70-80mph) shouldn't require a drop to 4 th gear! What kind of revs are you at when doing this?
My geared up 650 pulls well enough in 6th for decent ovetakes at all motorway speeds
However, when playing out on the back roads, using the revs & gears more, there is sometimes a slight momentary 'holding back' when pressing on & opening the throttle, presumably a result of lean running/emissions setup.
Where in the country are you, I think this needs better description if it's clutch slip, the revs would rise but speed wouldn't.