For reference, the optimal colour depth for VRPC performance is usually 32000 colours,
due to the way the software has been optimised. There isn't usually anything to be gained from 256 colour modes (quite the contrary) so I'm a little surprised by the finding that a 256 colour mode helped in the tests. In terms of resolution, performance drops with resolution/refresh rate, but when demonstrating a RISCBook (running on battery) at the Manchester user group last week, it beat the Iyonix at Artworks 2 rendering, even when running at 1600x1200 resolution. I will say we use a special MDF (monitor file) set up for the laptop LCD, which helps. And I'm sure Iyonix would win different tests.
To answer DGS, the difference in the hybrid machines is in choice of components and in configuration. Those of us who have spent time with VRPC know that choice of components has a huge impact on system performance (and device compatibility), as does how the Windows back-end is configured (and RISC OS/VRPC itself). This is why it takes a build time of about 24 hours for each RISCube/RISCBook that we sell!