Having used them (WP5.0 for SCO, WP5.1 for DOS, WP6.0 and WP6.1 for Windows, and supported WP5.1 and WP5.2 for Windows) my feeling was that ALL of them were rock solid ... UNLESS
You made the mistake of letting MS sabotage them. 5.1 and 5.2 for Windows were fine. Just a bit clunky, and I never had any desire to change from 5.1 for DOS.
6.0Win was great provided you ran it on Windows 3.1. Problem is, we were just introducing networking at the time, and MS slipped a bomb into the TCP/IP stack that killed it. It took 6.1 to fix all the "bugs" MS introduced.
And then, of course, MS sabotaged that with Office 95. If you installed 6.1 on top of Office 95 everything was fine. If, however, you installed Office over 95, well, ... the only way I ever found to fix the mess and get WP working again was "format c:".