well there's still a demarcation between the two, also separated by an expected price different of around 500 EUR. The XG438Q has only 120Hz and HDR 600 (edge lit local dimming) but is available imminently. The XG43UQ uses DSC so will support up to 144Hz and offer a slight refresh bump, and HDR 1000 (still edge lit local dimming) but will not be available for a while. apparently maybe in Q4, but i expect it won't be until 2020 given other delays in recent times.
DSC from the XG43UQ isn't supported from all graphics cards, and you'd need to consider whether you can achieve the extra refresh rate as well from your system at 4K. And then consider whether it's worth the extra 500 EUR to you.
It's about 300 euro price difference, the XG438Q seems to settle around 1200€. Both new Nvidia and AMD cards should support DSC afaik. 300 euros is nothing for a display that is noticeably better in a lot of key specs.