intel i9 9900k with nvidia rtx 2080 ti

For Premiere Pro CC, either one would be fine. You may, however, run into a different dilemma: It is very possible that both of those GPUs could be overkill for even your planned i7-9900K; in these cases, an RTX 2070, RTX 2060 or even a GTX 1660 Ti might be a better fit, depending on the media that you're planning on working with. You do NOT want your planned GPU to be much more powerful (performance-wise) than your planned CPU! (Unless you're planning to use the paid version of BlackMagic's DaVinci Resolve for color grading and much of your video editing work.)

In addition, be aware that Premiere Pro CC 2019 currently does not make any use at all whatsoever of the RTX series' new features, such as hardware Ray-tracing and Tensor core technology. As such, the RTX cards will be treated as ordinary CUDA cards for the purposes of the MPE GPU accelerated renderer.