Responsive editor - Size tooltip

There’s a cool option to pause rendering when changing responsive settings on complex pages in the Responsive editor.

It does not pause continuous rendering when resizing the frame (using the grey bar shown below). Clicking on an area in the grey ruler shown in picture will generate a single render at that point, which works well for complex pages, but we’re currently having to guess what width that will be (firefox at least).

Can we get a tooltip showing the PXs of our current mouse position?
Alternatively, can we show the px values of the major points so we can guess better.
Alternatively can we set our own breakpoints on four “views” to the left (under “current view”) I always use the same breakpoints but never the ones provided.