The ideal (and maximum) MTU value for Infinity is 1492, therefore the MSS value should be set to 1452 or less. If you set the MTU higher than 1492 you'll suffer from excessive packet fragmentation and possibly dropped packets which will make your connection appear to be unusually slow or broken.
The smallest MTU between two hosts is known as the path MTU. [ Need some text on PMTU discovery, MTU-vs-MRU ] Common MTU Values. Value: Link Type: 65535 : PPP max, Hyperchannel : 17914 : 16 Mbps Token Ring : 4464 : 4 Mbps Token Ring : 1500 : Ethernet, PPP default : 1492 : IEEE 802.3/802.2 : 1480 : PPPoE : 1460 : L2TP : 1454 : Optimal PPPoE-over How do I change the MTU size on my NETGEAR Wireless Router May 16, 2017 ADSL MTU - 1472 vs. 1492 | MyBroadband Forum Mar 16, 2007
May 22, 2018
Note: For information about why the MTU size is 1492 bytes, refer to the PPPoE Baseline Architecture for the Cisco 6400 white paper. The problem occurs because many web servers block ICMP messages, which causes the server to continuously send 1500-byte packets. These packets are dropped, and as a result, the requested web site does not load. Mss Clamping MTU Setting | Ubiquiti Community
Best DSL MTU not 1500? - SpeedGuide
Ethernet has a maximum payload size of 1500 octets. The PPPoE header is 6 octets and the PPP protocol ID is 2 octets, so the PPP maximum transmission unit (MTU) must not be greater than 1492. This is achieved with the configuration of IP MTU 1492 for PPPoE virtual-template interfaces. DM200 Support for 1508-byte MTU for RFC4638? - NETGEAR The default 1500 mtu on eth0 modem port doesn't seem to cause any issue. However if I trace the ATM side on the modem I can see 1500-sized frames going out and back (1492 payload) but the 1508 ones gets dropped (nothing going out at all). The wan port specifically refuses any MTU settings over 1500, as can be seen here: