I have been having the same issue for a long time. It's only when I try to stream PC games. I have lowered the resolution, lowered the bitrate, used monitor/display capture and game engine capture. I have even tried streaming my pc games through my elgato and it still shows up on stream as laggy. I have some scrolling text and clr browser plugins going even with all that streaming my consoles through the elgato runs perfectly fine. I've been over my encoding and video settings many times and have tried all the combinations I could find on the net while troubleshooting and still come up with the same issue. I'm starting to think its Win 10. Pretty sure my system can handle the load.
MoBo: Asus AMD 990FX Atx 4 Dimm DDR3 Tuf Sabertooth
Proc: AMD FX-8320 EIGHT-CORE 3.5GHZ 16MB 125W AM3+
Ram: Kingston 16GB 1600MHz DDR3 HyperX Red
Graphics: MSI GeForce GTX 970
OS: Windows 10 Home Premium 64-bit