Mixing GPU speeds for rendering?

[ledude]

Regarding GDDR5X (GTX 1080) and GDDR5 (GTX 1070)

If I am rendering with Octane with, for example, two 1080s and two 1070s (SLI is disabled), what impact, if any, will there be from mixing GDDR5X and GDDR5? Will Octane go only as fast as the slower GPUs? Does it matter?

My goal is to get the most CUDA cores for the money, but if the slower GPUs compromise the faster, then would there be less incentives for the 1080s? Would it be better to stick with four of the same GPUs rather than mixing them?

 

[iamacow]

As far as I know it will use every CUDA core available. So it doesn't matter mixing. However the slower card(s) will render sections at a slower pace. Since it does it the rendering in squares/block sections.