What GPUs shoud I get? R7900 or B70? (4x)

So i was thinking of getting a new setup. Currently I only have a single 7900xtx on an epyc platform. But do to high idle power consumption I want to change to something better. I saw a "cheap" pcie switch (plx88096) and decided that woud be a good idea to use it for my new cluster. (So gpus can still talk between them (p2p) ). But now I don't know what gpu i shoud get. I was thinking to use models like GLM 4.5 Air at Q8 (and when 5.2 air comes out to switch to that) so please help me get the right gpus for me. Also id like to achieve 40t/s.