Honestly, maybe .5-2 fps? Its not worth the hassle to return in my humble opinion and the 2070SUP will do you just nicely. You could OC it and gain those 30mhz.
As I understand it (I don't stream), NVENC streaming is very good quality on the Turing cards and doesn't use your CPU meaningfully at all. Or use the GPU for that matter, it's a separate hardware encoder on the GPU itself.
Likewise, 3600 is definitely good enough for mulitasking like gaming/discord/streaming on NVENC, and a whole lot more besides. With SMT enabled you have a whole lot of CPU threads to throw around for multitasking purposes.