4K120
Useful for modern game consoles and PCs. Every device in the signal path must support the required bandwidth.
8K60
Relevant mainly to compatibility and future-proofing today, but common on current premium processors.
External video processors
In advanced cinemas, source switching or video processing may sit upstream or downstream of the audio processor, changing how many HDMI inputs the processor actually needs.
Stability first
Reliable handshaking, EDID behaviour and firmware support often matter more than the largest printed resolution number.