The Power Challenge M (also known as `Power Indigo²') is roughly comparable to an Indigo²; this one only has an Extreme graphics board, not the faster Impact graphics. It's a very nice workstation nonetheless.
The R8000 is a very curious processor; it has a SPECint92 rating of 111.35 and a SPECfp rating of 310.57. In other words, its floating point performance is comparable to that of a 143MHz UltraSPARC processor, but it's integer performace is slower than a 75MHz SuperSPARC-II; SGI gives a figure of 360 MIPS and 360 MFLOPS peak. A very unmatched processor that was primarily intended for scientific computing and `number-crunching', not for use in workstations; I don't think it was on the market for very long. (People who needed much floating-point performance usually had to realize that their applications were crippled by the low integer performace.) Personally, I think that's very cool.
And this one isn't even an SGI model -- it's a Siemens re-labeled model, which means that it doesn't have the usual teal or purple skins, but a green one. (The Siemens Indigo²s have dark gray skins.)
I gave this box to Timo Kanera as a thank-you for helping me with my move to Bonn.