@Virgo In my original comment I wrote the following:

"To eliminate the possibility of hardware failure, I bought another ER7206 and got the same results."

The only thing I changed was the VLAN so internet would come through. 

@robinprice I have this same device.. and 1 fiber SFP module connected to 900/600 service, plus a cable modem connected using Ethernet at 600/10,, I get full speed on either of them..so you must have something wrong.

How does the isp router connect to the internet? PPPoE, IPOE..?

In particular what is the MTU of the internet facing interface in your ISP router ?

@crrodriguez I believe it connects via PPPoE. All I need to do is set the VLAN to 35 and I'm good to go.

I am also actually unable to check the MTU of the ISP router. Like I say, it's a terrible router/gateway and the big reason I'm trying to bypass it (I can bypass it, I just can't get full speeds).

@robinprice  well.. what mtu did you choose in the er7206 ?  it defaults to 1492.. try 1480 and report result. if still not working report exactly what device is plugged to the SFP port or what middleware is between the ISP port and the router (brand, model, etc)

@crrodriguez First things first; thanks for responding. I appreciate it.

When you say it defaults to 1492 I find that odd. Mine, on both devices were set to 1500.

MTU = 1492:

530 down / 417 up

MTU = 1480:

531 down / 428 up

Both tests were from a hard wired Apple TV.

I then took the laptop to the router and hard wired.

Both 1480 and 1492 gave around 680 - 700

@robinprice 

We are not getting anywhere,,  probably because incomplete inforamtion from your side, so let's try again

- A PPPoE interface cannot use an MTU of 1500 (unless the device AND ISP support/advertise

bigger packet sizes),. On this case the er706 does not advertise such capability (it is yet another missing feature ona supposed business device)  this reveals you are not estabilishing a PPPoE session from the er7206 but on some middleware device.. (which device ? brand , model name) if you can do that and "dial" up directly from the router it might help. It is for this case only that my suggestion of an MTU lower than 1492 applies. as this is a very well known problem, packet fragmentation or MTU discovery issues will ruin TCP performance..

if you are just plugging the ISP device and getting into vlan 35 and it works then it is IPoE most likely and this recommendation does not apply.

- if running an speed test, use the APP , not the browser to ensure you are measuring the right thing. do not use an IOT device, wifi or some USB network adapters, most of them are crap except higher end ones.

-  ensure you are testing the correct thing, that is the speed from your location to the ISP border.. not to some random server because you ain't actually paying for that.

- I am assuming hardware accelartion to be enabled but disabled shouldn't break havoc either.