I have an overclocked i7-9700k as well as a EVGA RTX 2060 KO, so I think that I can shed some light on both your CPU and GPU question.
My 9700k is overclocked to 5.1 GHz on all 8 cores; keep in mind that I seem to have a better chip than most so you might have trouble getting that last 100 MHz. It also might help that I have a 280 mm AIO keeping it nice and cool, so that might have a positive affect on the stability of my overclock as well.
I do folding@home calculations 24/7 on my 2060 KO and I have the fan speed set to 100% (about 3300 RPM) so long as the software is running . I've been doing this almost uninterrupted since April 2020 and haven't had any issues. Of course, I probably won't hang onto this GPU for 4 years like you plan to with yours, but I haven't seen any issues as a result of doing this thus far.