We use a G4 mini as a workstation (with a 21.3" Samsung flatscreen). Works fine with maxed out RAM, but isn't very fast with rendering, of course. Except for OpenGL, the processor is the most important speed factor in Archicad. A Dual will speed up Lightworks and Artlantis, and simultaneous use of other applications as well. When the Universal Archicad comes, it should run much faster on the new Mini.
The Radon9200 graphics card in the G4miniis fast enough for Archicad 9's modest use of OpenGL in 3D navigation anyway. And if you look at Macfixit's coverage, the new integrated graphics should at least not be significantly slower than the old mini:
http://www.macfixit.com/article.php?story=20060228103152918
As usual, I think to max out RAM memory is the most important issue.
AC4.1-AC26SWE; MacOS13.5.1; MP5,1+MBP16,1