I was at E3 Nova theater when they talked about FH4 and they said that 60 fps will be available on the Xbox One X in 1080p resolution, which I would take the 60fps 1080p vs the 30fps 4k any day for racing.
With the right PC setup you could get 60 fps in 4k, or even higher FPS in lower resolution’s. Ultrawide is available in FH3 and FM7 on PC as well, so I would think/hope that would continue with FH4.
I know someone who gets 140 fps in Ultrawide 1080p for FH3 with a 1080ti and a i7 8086k. I get 90 to 100 fps on standard 1080p with Ryzen 1700x and Vega 56. These are for Highest graphics settings, which you can adjust on a PC vs an Xbox. You can get higher FPS by dialing down graphics settings as well.