Here's a snipped directly from from the Octane Render FAQ:

https://home.otoy.com/render/octane-render/faqs/

...

"What are the hardware requirements for OctaneRender?

OctaneRender requires a CUDA enabled NVIDIA video card. An up to date list can be found here.

OctaneRender can run on most CUDA enabled consumer video cards, instead of only on high-end Quadro cards that most other solutions and middleware require, but it is specifically optimized to run on Kepler (GTX 6xx, GTX 7xx, GTX Titan), Fermi (GTX 4xx, GTX 5xx) and Maxwell GPUs. Kepler GPUs allow a higher texture limit (256 compared to 128 on Fermi) and are more power efficient and silent than Fermi cards. GPUs from the GeForce line are usually higher clocked and render faster than the more expensive Quadro and Tesla GPUs...."

Noting, that this was put up quite a while ago already. GTX9xx (and other) cards are working well, too. Currently they're working on full support of the new Maxwell technologie (Titan X, GTX 1080 ...). These crades are already working, and that really well, but they're still not optimized yet. Once they're fully supported, the benefit will be even greater.