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That would explain it! I'm a bit bummed since I was very excited at the idea of using Octane as my main renderer, but I guess it'll be useful anyhow.

Thanks for the answer and for this excellent piece of software!

wow! so glad i 'tripped' on this thread, thanks t_3

why a 580 with 3GB?? couldn't they just do a 590 with 3 GB??

why do you have to choose between 512cudaX3GB and 1024cudaX1.5GB???

can't understand certain things

unless there is some technical reason which i ignore

@KaroBastardKiter :

why a 580 with 3GB?? couldn't they just do a 590 with 3 GB??

why do you have to choose between 512cudaX3GB and 1024cudaX1.5GB???

It is probable that building a card with two GPUs sharing the same VRAM area would be difficult.

Currently GTX 580 3GB are not built by Nvidia, but instead derivated from the original concepts designed by Nvidia, by just adding more VRAM. So, they are just enhanced devices, but not revamped devices.

GTX 590 3GB are originally built by Nvidia. They are like double GTX 580 1.5GB on the same board.

A GTX 580 3GB has one GPU with 512 cores and 3GB of VRAM dedicated to that GPU.

A GTX 590 3GB is in fact made of two GPUs of 512 cores each with 1.5GB of VRAM dedicated to each GPU.
So, it gives more computing power (1024 cores) and will render twice faster as a GTX 480, but the real amount of VRAM usable to build a scene is 1.5GB.

So if you render large scenes like city scenes or landscapes, or even interiors with many objects and textures, you will be soon limited by the VRAM amount of 1.5GB. You must also know that the amount of VRAM required is dependent on the resolution of the rendered image. So, if you have to render a very high resolution image (8192x4096 for example) for a poster or a billboard, it may require much more VRAM than a render at 1280x720 or 1920x1080.

Unless you aim at animations (simple animations as currently the export/load time for animation is very long for most packages) or simple objects, it is better to choose a large VRAM amount instead of a high rendering Speed.

Anyway, for stills Octane works fast even on one GTX 580 ! If you can, use a separate card for display (to avoid your screens eat some VRAM amount on your GPU dedicated to rendering), and One or more GTX 580 3GB for rendering. It is a very comfortable setup.

merci roubal, very clear explanation

Sorry, if that was mentioned before - but i'm wondering what will happen if i use a GTX 580 with 1,5 GB RAM and the textures/render size is too big. Will Octane crash or will the render be slower because of swapping to hard drive (but finally i will get my rendered picture)?

It won't run. All the data needs to fit in the available vram. You would have to compromise somewhere ie reduce the film resolution, fewer textures, or fewer polys or a combination.
1.5 gb may be OK depending on what you do. If you are doing archviz it probably won't. 2 or 3gb would be better requiring 12 and 16 or 24 gb sys ram respectively.

Thank you for the info, pixelrush. So i'm going to order an EVGA GeForce GTX 580 with 3072 MB/384 Bit to be prepared for bigger projects and keep my GeForce 9800 GT/1048 as the UI display device.

Does anyone know what the best mobile card is? I was hoping they would be covered in this chart as well. I just got this:

http://www.asus.com/Notebooks/Gaming_Powerhouse/G74SX/

It has a 560m. I know it's not great, but am not sure what the alternatives are for mobile cards. the 560 is nice for big scenes because it has 3gb vram, but is lacking in cuda cores. Any GPU recommendations for laptops?

Thank you very much for your chart and testing.
I have been able to upgrade at optimum cost!
Found a GTX470 at leboncoin.fr (works well in France)

I am excited of the new GTX 680 with unbelievable 1536 CUDA-Cores . That are 50% more CUDA-Cores than a GTX 590 has. And the GTX680 is also cheaper. Damn, i want to have the money to buy it .