I decided to check everything myself. Quadro p400, even in PCI E 3.0 x2 mode (!), because of the peculiarities distribution of lines of my Asus B450 strix f motherboard, it normally encodes a stream at 1440p*60 20000.
Quadro loaded at 40%. My 1070, in TSW, with 60 fps, was 100% loaded on some maps, and the stream began to lag. I had to reduce the graphics and set the lock to 45 fps. Now I have checked and can stream the same cards at 60 fps and with higher graphics settings. Video 1070 is loaded at a maximum of 80%.
In PUBG, when streaming from the main video card, there was a feeling of a small but annoying input delay, or as if the registration of hits was getting a little worse when streaming. Now this effect has completely disappeared.
The main video card works in x16 mode, as usual.
in Xsplit it became possible to simultaneously stream to YouTube and Twitch, also in 1440*60 (I did not know that Twitch can take 1440p) with a different bitrate for each site. Loading Quadro at the same time - stably 75%.
This is not an ideal solution, I will change the motherboard so that Quadro can work at least in x4. But I do not regret the $ 50 spent