Barty1884 :
IIRC, it's going to be roughly comparable with an RX580, but had a bit more of a VRAM buffer (like 9-10GB vs the 8GB in a 580).
Of course, it's not directly comparable..... but it's going to be in that approx performance bracket.
The XB1X GPU might be capable of more, but it's likely limited by the slower Jaguar CPU (performance-wise, somewhere between 1/3-1/2 of Ryzen performance). I wouldn't be too surprised if the "theoretical" performance of the XB1X was in 1070 territory, but in real-world performance, RX580 range is where it's at.
This is not entirely true, the GPU processing will not be slowed down by the CPU, however when it comes to CPU intensive games (or intensive CPU parts of games) such GTA5 then you run into problems, and this is why GTA 5 is locked to 30fps on PS4 and Xbone one, if a patch was released for the PS4pro and Xbox one X, you will not get any better fps even with the overclock on the CPU's its not enough.
Again to prove my point, a GTA 5 patch could give better anisotropic filtering for PS4pro and Xbox one X, along with overhead powerline shadows and and maybe some other small improvements, all of this is will have no effect on the CPU processing as its processed in the GPU, add more traffic and pedestrians then you have problems as that requires more CPU power, so the real issue here is framerates dropping or being locked over the CPU not because the CPU would be holding the GPU back.
Developers will scale back with CPU processing tasks when making these games for consoles so the game will run at a locked 30fps and that was proven with GTA5 before and Assassin's Creed Origins, GTA5 traffic and pedesrians where cut back compared to the PC, and they locked the fps to 30, Assassin's Creed Origins runs at a higher (dynamic resolution) than what was possible on the older versions of the consoles, the game runs at 30fps with drops to 26fps at parts.
So we see an increase GPU power and whats on screen, the CPU is the same old CPU even if overclocked its not a huge improvement, its the same as an overclocked i3 2100 not the newer AMD processors which can easily outperfrom the old server AMD CPU which is the JAGUAR.
So the gpu is not being held back, as it processing all graphical tasks, the CPU processes all the CPU related stuff, yes they work toegther but they have different jobs, if GTA 5 runs at 30 fps its over the CPU not the GPU and the reason it runs at 30fps.
This statement would be more true, the CPU is holding back better frames per second not the GPU.
Final word, build a rig stick a GTX 1080 in with an A10, you can max everthing, but it will run mostly at 30 fps, does this mean the CPU is holding back the GPU? no it doesn't, does this mean the CPU is not fast enough to do its part to deliver 60fps? yes it does, the GPU has delivered on its part with delievery all of its graphical processes and is not being held back.