What "no bottleneck" means here
A graphics card can only show its full speed if the processor feeds it frames fast enough. If the processor is too slow, the card waits, and you pay for performance you never see. This tool picks the processors that keep the CPU and GPU within about 10 percent of each other, so neither one wastes the other.
The pairing depends on resolution. At 1080p the graphics card finishes frames quickly, so the processor matters most. At 4K the card does far more work per frame, so a mid-range processor is plenty. That is why the lists differ for 1080p, 1440p and 4K.