I switched fully to using SGI gear a year ago. My main system for day-to-day tasks.
At first, I used a Tezro. To me, this seemed the ultimate in performance and daily-use however because they are rare and expensive.. I stopped using it. That and it does not seem to like hot environments as it gets in the summer here.
Then I used a 300mhz O2 with a quieter fan. It ran well even in a hot room with relatively lower electric consumption, but using rdesktop to other servers seemed to be choppy with the video. I needed rdesktop to be able to access MS Office, Skype, and as a Cisco VPN client for my work (no way around that). Plus, the O2's max resolution is subpar.. 1440x900 in my efforts. I really need 1920x1200 to work effectively in my trade. Dual Monitors are rare to get with an O2 as well.
So, I went to a 300mhz Octane.. later upgraded to 400mhz (didnt really notice a difference from 300-400 though) with dual Vpro video boards that give me dual screen with high resolution across 27" LCD monitors. I do everything on it. Except MS Office, and when I need to do some financial website browsing or ebay to buy more SGI gear.
For 'windows' accessibility that looks 'somewhat' native to IRIX I use an Intel ComputeStick (99$) that is a full featured PC smaller than a PC mouse powered by USB (draws just 5 volts). I just dangle it on the back of the Octane and that is my 'Windows apps' device as well as a way to get USB access for things like photos from a camera. Using Windows Server 2003 on the ComputeSitck (in a VirtualBox VM, etc..), you can utilize SeamlessRDP to launch applications in their own window versus a full desktop session. With rdesktop/RDP, your user home directory on IRIX can be directly accessible to the windows application your using. So all the IRIX apps (and GNU apps) are at my fingertips as well as an integrated Windows application environment too. (You could power the ComputeStick from inside a system from a molex power cable too.. then stuff the ComputeStick inside. Sort of like a modern SUNPCi card from SUN Microsystems that allowed for Windows integration on the Solaris desktop).
Hopefully my experience can help you
If you plan to use the system daily, I do suggest an Octane. Octane2 if you can find one.