[Trippynet]

A lot depends upon the spec of your teal Indigo 2s. I've run 6.5 on Indys (133MHz R4600 with 128MB of RAM) and it wasn't a great experience, there's just too little RAM left after the OS has booted and performance wasn't great. However my Indigo2 originally had 256MB and ran 6.5.22 without any major problems, of course more RAM is always a good thing!

Hence, I'd say 256MB+ to go for 6.5.22, and if you have 128MB or less, maybe 5.3 or 6.2 would provide a better experience. Robespierre is right though that IRIX was quite fragmented before 6.5 came out, so you'll need the appropriate disk for your systems if you do decide to run an earlier version. Also, it'd be useful to know what CPUs your teal Indigo2s have as there was a big range (100MHz up to 250MHz).