the machines are fit for purpose
Let's start from the very beginning: Besides the other hardware components, the most important factor for the Octane Plugin is the Graphics Card (GPU).
Now let's open the subject a little more: We have explained how Octane works in this section. From the moment the Octane passes through the render stage (the sampling stage), the whole load is on the GPU. In this case, the only factor that determines the speed of rendering is the GPU. You might think: "I should get the fastest GPU". Yes it is a correct proposition. After all, the fastest card is always good. We still recommend you to choose hardware according to your purpose. For example, if your business is Archviz, our recommendation will be a powerful GPU (and a computer). Know your goal before choosing the best hardware and do your research regarding to this purpose. Because this subject is very complicated and has a lot of variability.
Since we do not specifically say that you choose this or this hardware, at least we can direct you to the right places in this matter.
First, we recommend you to visit the Octane Bench page. The View Results section on this link is also very useful. You can see how most of the Nvidia cards perform on Octane. There are real user data about how Octane shows performance in both single and multiple card usage. You can also download the Octanebench software and see how your own GPU is performing.
Also, the hardware topic in the forum is a very popular. Many users share their experiences and recommendations. Take a look.
Finally, you can go to this site that makes many hardware comparisons in detail and see the GPU results.