As an anecdotal evidence from Forza 5, which runs in 1080p & 60 fps;
XB1 has at least 5-6X the power of X360 hence the following:
720p to 1080p : 2.25X
30 fps to 60 fps : 2X
Totals to : 5.5X
We don't quite see much of an improvement in graphic fidelity otherwise. This, being a first party title, 6X unoptimized first gen theoretical performance increase seems adequate.
I suspect the increase might be higher, around 8X but it's the system bottlenecks, the virtual machines and the reserved CPU/GPU cycles that are keeping the theoretical performance down. So 6x performance increase may be more realistic.
Playstation 5 vs XBox Series Market Share Estimates
Regional Analysis (only MS and Sony Consoles)
Europe => XB1 : 23-24 % vs PS4 : 76-77%
N. America => XB1 : 49-52% vs PS4 : 48-51%
Global => XB1 : 32-34% vs PS4 : 66-68%
