iray needs neither SLI nor CUDA?

Is it true, that iray does NOT need SLI or CUDA for GPU rendering? though it´s recommended…
octane is said to render on every GPU available in the environment (but needs CUDA cards)
octane will work with all the power available even with completely different cards.
does this also apply to iray?

iray does not use SLI. You may leave SLI active, but it is recommended to deactivate it, since performance tests indicate that SLI may slow down the rendering process.

On the contrary, it is strongly recommended to run iray with one or more CUDA GPUs. Quadro GPUs are strongly recommended. Non-CUDA GPU cards will not work, iray will simply ignore them. iray can run on the CPU(s) alone, but it is really not recommended to do so - iray’s magic is possible thanks to the CUDA technology, the CPUs alone are too slow.

By default, iray will use all the available GPU(s) and CPU(s) simultaneously. However, it is recommended to disable iray’s CPU support when using CUDA GPU(s), because the CPU(s) are very likely to create a bottleneck (they are slower than the GPUs).

You can mix different types of CUDA GPU models on the same machine, and iray will use them all. A typical professional configuration used to be 1x Quadro 5000 + 3x Tesla C2050. Today you can purchase even more powerful cards. However, be warned that each card has to fit the whole scene in its memory, so it won’t make any sense to couple a 1GB card with one or more 3GB cards, when your scene requires for example 2GB: the first card will set the overall bar to 1GB therefore iray will fail while trying use the GPUs. Likewise, it won’t make much sense to couple cards with a very large gap of computational capabilities - the slower cards might create a bottleneck for the faster cards.

Hope this helps, have fun with iray!