Hi Peer, there hasn't been any changes in panning behavior in MoI v5 compared to v4.

The available methods to pan other than the viewport button are:

MMB drag
RMB drag in ortho views
Shift + RMB drag in any view
Alt + LMB drag in ortho views
Alt + Shift + LMB drag in any view (Maya and various compat)
Alt+RMB drag for ZBrush compat if [View] AltRMBPan=y is set in moi.ini

- Michael