Why not get a CM4 with the IO Board? PCIe on the regular Raspberry Pi seems too niche for them to consider.
My most recent one will have 6x raspberries with really nice heatsinks for the 4: http://move.rupy.se/file/pi_4.jpg
The cost of the CM and the ergonomics of the design makes this more expensive than going full Intel Atom!
And the Gflops/watt is exactly the same.
It's still hard to find both the IO Board and CM4 in stock though :(