It works well for me - just tested on Windows. Could someone please try to reproduce this on Mac, too?
Try it while the mouse is over a slice viewer. You may also clicking in the viewer before starting to use shift+wheel (you can do right-click, to not erase anything at the click position).
Slicer-4.10 has many very important improvements and hundreds of fixes, so I would definitely recommend it over Slicer-4.8. Please report any specific problems that you encounter.
Overall performance should be greatly improved (in some cases up to a factor of 10x), but since rendering pipeline in underlying VTK library has been completely reworked, utilizes and requires most modern OpenGL API, in some cases we observed slight performance decrease (such as slice browsing performance may be slower by 10-20%, especially on older systems). Try to upgrade your graphics drivers and let us know about any specific issues.