I was a somewhat heavy user of IE4, IE4.5 and IE5 for Mac both back when they were new and a few years later, as recently as 2005 or 2006 when I still had my TiBook and was dual booting it, my blue-and-white G3, and later on, my PowerBook G4.
Of all the browsers for Mac OS 9 that existed until Classilla came onboard and fixed a few but not necessarily all of WaMCoM's issues, it was probably the best and the most likely to either successfully render a page, or at least fail gracefully without either requiring you confirm that you received 17 errors 17 times (iCab) or simply crashing (Netscape/WaMCoM.) I also found it to be a lot faster than the newest versions of Netscape and Mozilla that ran on Mac OS 9, though maybe that was an age difference, I do believe that WaMCoM and the newest Netscape for OS 9 were a few years newer than IE5 was.
Of course, the other thing is that IE5 ran on PPC systems running OS releases as old as 7.6, and the Mozilla/Netscape/iCab compatibility changes a bit from 7.6 to 9.2, I never really looked at browsers for OS 9 that much because I spent relatively little time on the Internet in OS 9. I was usually booted into 9 (specifically 9, as opposed to 8.1 on my iMac/233 when it was my only computer, or 7.x and 8.1 on my various beige PPCs) it was for some kind of productivity app, as opposed to network access.
If you're designing a page targeted toward old Macs, I'd say to make it visually as simple as possible, maybe dig out your copy of Claris HomePage 3 and use that? That'll get you pretty good results on version 3/4 web browsers, and something that's likely to be mostly usable on version 1/2 web browsers, just depending on what stuff you end up using.