I personally have never seen a dual system rig with just one PSU. I would go with the dual 750w and call it a day or one 600w and one 850w to leave room for the main rig upgrades down the line.
Ryzen 7 7700X, MSI MAG X670E Tomahawk Wifi, Corsair DOMINATOR® TITANIUM RGB 2x16GB DDR5 DRAM 6000MT/s CL30, Sapphire Pulse AMD Radeon RX 7900 XTX, Corsair HX Series™ HX1000, Corsair MP600 PRO NH 4TB