Is the 600Mbps over wifi or ethernet cable? ~600 is the maximum you will get on a Hub4 as its only wifi5 (its just "physics") - you would need wifi6 to get the maximum speed. You should get ~960 on a single Cat5e/6 ethernet cable connection
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.