I think I found my answer. The WAN port on the SMC7004ABR 750.5432 appears to be a 10MB Half-Duplex. Even though the LAN ports on the unit are 10/100MB Full-Duplex Auto MDI/MDIX.
I've discovered this just today when I was setting up my x
DSL with a ZyXel 660R unit and it's diagnostics told me I was connected to the SMC WAN port via 10MB Half-Duplex. The LAN port on the 660R is a 10/100MB Auto MDI/MDIX.
I'm going to bet that this is a good chunk of the issue I was having with the Comcast and my Motorola SB5100 when Comcast went over 4MB.
Motorola tells me that the SB5100 is completely transparent to the cable system and will pass a full 38MB/s cable system max. The Ethernet port on the SB5100 is 10/100 Full-Duplex.--
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