RFC 4638 (MTU 1508) possible on (stock) RT-AX88U or RT-AX92U ?

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I enjoy a gigabit fiber connection up to a theoretical speed of 977 mbit/sec. Currently, I have MSS clamping enabled (MTU and MRU are set tot 1448), because the stock firmware GUI will not allow me to set MTU / MRU values above 1492. This will give me up to about 928 mbit/sec download speeds.


My provider Freedom Internet (Netherlands) supports RFC 4638 (MTU 1508) for sure. If possible, it is recommended by their tech support to use RFC 4638. They tell me to: switch on jumbo frames, use MTU 1500 on LAN, use 1508 on raw WAN interface. This would enable a PPoE tunnel of 1500 and eliminate the need for MSS Clamping.

Is this scenario possible on the RT-AX92U (or RT-AX88U)? If it would mean to switch to Merlin or use SSH into the Asus router, this would not be an issue for me. How much would the speed benefit be?
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