So GTX580 for rendering and onboard graphic for display adapter Correct?
Correct
Stacking cards : you can get risers
You can get extender cables so the cards sit outside your PC box. I wouldn’t worry about it unless you are building a render farm and wanting more than 4 cards in a single PC.
Maybe but you can get the GTX580 for 200€ now
The 600+ series cards are quieter, use less power, incredibly reliable, and allow you to have over double that number of texturemaps loaded. Whilst a GTX 580 would be quicker than a 660Ti (at roughly the same price???), you’d need to research if the increase in speed warranted the other disadvantages.
Does the graphic card memory only limit the textures beeing loaded in
the scene or the imported geometry polygon count?
Yes, polygons take up VRAM too. From memory, I got around 16 million polys into my 2Gig card. If you are instancing geometry, you will get far more polys in the scene (since only one copy of the polys are in your card)
I’m now considering the GTX 680 for Mac and Octane. However the 680
only has 2MB memory. So, if this isn’t enough processing power, I’d
add a second 680. Any thoughts??
It depends what “isn’t enough processing power” means? Whilst tweaking the scene and materials, you are moving sliders on-the-fly and getting immediate feedback in the Viewport, so whether you have a lot of processing power or not doesn’t matter too much. It’s really just for the end product render where it makes a difference. But yes, if one 680 turns out to not be enough, you could add a second (assuming your hardware supports that).
All this talk of multiple 680’s seems strange to someone very happy with a 550Ti But if I was rendering for a living rather than coding, that might be different.
Paul