CenturyLink gigabit PPPoE/igb, are there still performance issues?

[Mel Pilgrim]

I have CenturyLink GPON service, which uses PPPoE.

I've read about the performance bottleneck with PPPoE over igb 
interfaces limiting throughput to only a few hundred Mbps unless run on 
fairly capable hardware.  Caveat: the posts that discuss this issue are 
a few years old.

The hardware I have is a Xeon E3-1245v6 with igb interfaces.  That seems 
like it should be beefy enough to handle a gigabit of PPPoE.  In 
testing, I get 800+ Mbps when connected though the router provided by 
CenturyLink, but only 350 Mbps when connected directly to the ONT.

If I add an em-based NIC, will that work around the issue?  Is a 
cxgbe-based NIC the better choice?