Right, I wanted to start this topic to collate what JohnFredC wrote here about having middle-click option with my own idea of a smoother right click panning control.
Ok, so this is the current interface of those settings in MP 0.38.3
(click on screenshot to enlarge)

Ok, now and this is my mock-up of the two new options that could be added to this layout setting:

So to explain:
Middle click : 'do nothing' and 'move picture' <----- so if the 'move picture' is enabled here, then default switch mode (viewer>>fullscreen) get's auto-disabled
Right button + CTRL : 'do nothing' and 'move picture' <----- so this is needed because currently if I pan in viewer/fullscreen with just right mouse button alone then often the right-click context menu often displays which is an inconvenience when doing panning but nonetheless is still an important feature.
So I think the current "Right button" should remain for 'move picture' but also add the above requested 'Right button + CTRL' for the same 'move picture' so that if both are enabled as the same, then 'Right button + CTRL' would just offer more accurate (context-menu free) panning.
This is something to consider for a next major version, maybe