You're going to be limiting yourself actually just by having the 1050ti in there, because you're now running at PCIe3.0x8 instead of x16. Take the 1050ti out entirely, unless you have other specific reasons for it (such as 5+ monitors).
The reason being, Nvenc is a "free" encoder. It exists as separate silicon on your GPU, and its sole purpose is to encode video. Those two cards have the exact same silicon for the encoder, meaning even though your 1050ti may not be utilized for gaming, it's only able to do encoding just as well as the 1060 which is being used.
Add on to that fact, now you're asking one GPU to send its frame buffer over the PCIe bus to the other GPU, and both cards now only have a x8 connection to perform this on now.
Your best bet is to use the Nvenc (new) encoder, with only the 1060 installed. This lets the GPU send its composited frame straight from VRAM to the encoder, without going across the PCIe bus to do it. Plus, you get the benefit of a full x16 connection to your CPU for less potential bottlenecks (there is a LOT of data being sent back and forth just for normal scene compositing).
I will mention though... if you're bringing this up because you're having performance issues with using a single card for Nvenc, please post a log file of a recent recording/streaming attempt
so we can possibly help troubleshoot the issue.