Some early raw samples are up now, so I spent an evening with them. Method, for what it's worth: downloaded the ISO series from two sources, resampled both those and my own A7 IV files to the same 24MP output, same Lightroom settings with noise reduction off, same lens class.
At ISO 6400 I honestly can't separate them. At 12800 the A7 V might be very slightly cleaner in the deep shadows, but that's within what I'd put down to different raw processing. Base ISO looks very close as well, and pushing shadows four stops I couldn't see a difference either.
That's about what I expected from a sensor designed around readout speed rather than noise. Nobody should buy this for image quality. If you shoot things that move, the readout and AF are the reason. If you shoot stars, keep your money. I'll revisit when someone with proper test gear publishes read noise numbers.