From you posts you seem to want to try to build this on day1. I guess you could buy the chip the first day if you think it is going to be hard to get but there are things I am waiting to see how they solve.
The normal 7900x will likely outperform the 7900x3d in application that can not use the the cache memory. Since the cache cause some of the core to have lower boost clocks and the 7900x can boost all its cores to the same level.
What my key concern is how do you get application on that can use the 3d cache on those cores and applications that can not use the cache on the other cores. In simpler cases maybe the OS could do it. But say you get a game that can run multicore. Now the game developer must tune their game to use this processor.
You could get extremely random results if the processes in the game are not consistently allocated to the most effective core type. Many game developers will not bother for such a small percentage of users who buy these chips. This means some game benchmarks on this chip will be very inconsistent.
What I suspect is it will be a few months after these chips have been on the market before we see truly what the real potential is.