Hi Andrew Le Bihan,
1.) In Version V6, I don’t feel that Cycles is presently responsive enough for previewing mid*/large projects. Understandably, the emphasis was placed on total rendering time. I wish it were checked with more larger projects. I understand that there is a tradeoff between total rendering time–and responsiveness.
At any time, it’s really easy to crash Rhino with a 3.4Ghz quadcore/GTX 1080/ 16B GB RAM/ SSD/ PCI3 Bus. Rhino will usually go white on you in warning. If you add one more event onto the heap, it’s likely going to come crashing down.
2.) As Holo (and Nathan) pointed out, textures such as 4096’s, add to the slowness. I use these only where necessary, where I need texture over distances. There are 2 of 4906’s with bumps, 3 of 4096x2048, 1 of 2048, and about a dozen small textures. I feel that this is a texture load that is much smaller than many modern video games, which often have complicated shaders, which do such things as billboarding, additive lighting, and waveform luminance animations.
3.) Cycles will crash on GPU, where the CPU rendering will succeed–even under the checked/observed memory of the video card. This kind of Rhino crash will not reliably produce a Rhino crash dump.
4.) There are texture mapping inconsistencies in non-Cycles modes, such as this problem with the Brick Materials. AFAIK, Cycles gets this right; Rendered Mode does not. As I remember it, a non-cycles raytrace of this will not show this mapping.
(Note: In this screenshot, a material swapped with an grid material for scaling and aligning materials with unclear biases. Oddly, the ability to do that could be a feature.)
5.) While V6 view speeds may be improved over V5, IMO, the non-Cycles display speeds should be a lot faster for what is being done. I have experienced how the non-Cycles display speed will present an issue for working on the kind of projects that 64-Bit and Grasshopper’s power and promise offers.
( I am not sure why Rendered mode shows bumpmaps as a blue haze over the diffusemaps; it doesn’t really help.)
*I don’t think a small diner with a low-polygon interior is a large project.
I have parts in the living room to refit my computer with 3.9GHz 12-core, 32GB goodness, but a 70-100% increase in single-core computational power will only go so far.