There is clearly a hardware or software issue on the old PC that is limiting the network speed. To see if its hardware related, connect the old PC byCat5e/6 ethernet cable directly to the Hub and see if the speed increases to max If it doesnt, put the Hub into modem mode and try it again. If it still doesnt get up there, reboot the pc into safe+networking mode and try again. See what that gets.
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John
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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. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.