Some good news -
I uninstalled 5.0.2 this morning, and installed 5.0.3 and it has worked for 12 hours without a single hang.
I am not plugged into an external monitor today, as I am on a customer site, so I'll see how tomorrow goes when I'm on the external display.
I checked my download, and it was not corrupted (did a cmp) so perhaps I did not uninstall it properly the first time?
Hoping to report back good news this time tomorrow 
One observation - I now get large black squares flicker behind the cursor from time to time, this never happened on version 4 - 5.0.2 for me ... it has just started with 5.0.3, although I see a separate thread for that ... I might go back to 5.0.2 after all.