If your Intel Comet Lake furnace and your NVidia Ampere furnace are both pulling maximum amperes at the same time, you may very well need an 850-watt power supply. The 660-watt PSUs that I've used for most of my family's PCs in the past decade might not be adequate for that load.
What this means for me is that I will swap my Focus PX-850 power supply into the new PC that I'm building to house a yet-to-be-released graphics card and I'll put the spare SS-660XP2 Platinum in the old PC since it "only" has to power a Vega64.
I'm willing to pay for the extra electricity for the graphics card and the air conditioning while gaming. I am much more concerned about getting adequate case ventilation to handle that much heat from a graphics card without resorting to dustbuster noise levels.
Going forward, I will also revise my current usual PSU recommendation of a Prime PX-750, which has the same compact 140 mm depth as the entire Focus series. The Prime PX-850 and 1000 take up an additional 30 mm.