The only reason we’d invest in the 9900K right now would be if we played games such as StarCraft II full time. There's a few titles that do play noticeably better with the Intel CPU, in StarCraft's case in complex late game 4v4 battles. Likewise, you’d go Intel if you needed every last frame possible, but short of that the 3900X is the better choice.
It’s worth remembering that we’re seeing little difference at 1080p with an
RTX 2080 Ti. This means using an RTX 2080 will more than halve the margins seen here and we know because we’ve looked into it. Then with an
RTX 2070 or
RX 5700, performance will be identical. Alternatively, if you play at higher more GPU-bound resolutions, you’ll find the same thing, marginal difference in terms of gaming performance.