As the title sais i want to watercool both my cpu and my gpu but my h500i only supports 280 mm rads and i don't know if the thickest rad out there with fans in push and pull config can cool my cpu and gpu (rtx 2070 and a r5 3600x in the summer)
Usually exotic cooling is only needed for record seeking overclocks.
The requirements for the rumored 3000 series ryzen are unknown.
But, today, ryzen does not overclock that well and better temperatures amy not be worth that much.
On the RTX2070, realize that
Graphics card vendors bin their chips and use the better ones in factory overclocked versions
that they can sell for more. You may be able to OC more, but then again, perhaps not.
They try to differentiate by adding cosmetics and fancy coolers which also sell for more.
I do think you get fair value from a modest factory overclocked card.
If you need more performance, they buy a higher tier card in the first place.
In a good case, you may well find that air cooling does the job for less, allowing you to spend more on intrinsically faster components.