Hmm, still haven't found a diagnostic (IDE) cd image, but I tried
OpenBSD/sgi 3.7:

Obtaining /bsd.rd from server                     
5968528+306992 entry: 0xffffffffa0100000
ARCS32 Firmware Version 1.10            
SR=34010080
Found SGI-IP32, setting up.

... and there it hangs :-(

Guess I was lucky that my initial NetBSD installation just worked (tm)

Martin