however the "device" speed powered by speedtest.net will not surpass 2-300 Mbit down and ~50Mbit up.

How is the device conducting this test connected to the Gateway (Ethernet or Wi-Fi)?

If Wi-Fi, how far away from the Gateway are you when conducting this test?

If Wi-Fi, can you conduct the test on an Ethernet-connected device?

What kind of latency are you getting when not under load?

I have my home server which is acting as my router connected directly to the BGW's 2.5G Ethernet port. The tests are being run directly on the server running Debian with Firefox as the browser. I am getting ~14ms latency unloaded. Thank you for responding!

What kind of hardware are you running Debian on?  Specifically what is the Ethernet Interface, and what connection rate is associated with that interface?

It is an HP Proliant DL560 Gen8 with quad Xeon E-4600 processors, 256GB ram, HP 560 SFP+ with a 2.5G Ethernet transceiver installed. I am also using IP passthrough on the BGW. Both the BGW and Debian are showing a 2.5G link speed.

There have been a lot of issues with the BGW320's Ethernet ports syncing properly with a variety of Ethernet controllers, and the 5 Gbps port on the Gateway is the most problematic.  If you're seeing it sync at 2.5 Gbps that probably means that it synced up clean, although there are people who see it sync up at 1 Gbps and then the interfaces drop offline intermittently.  

Things to try for fun, purely for diagnostic value:

1) Try a 1 Gbps port on the Gateway either with the SFP+ or a 1 Gbps native on the Proliant

2) Try inserting an Ethernet Switch (even a 1 Gbps one) in line

Either (or both) of these should get you tests up to 940 Mbps.  If they do, then the issue is with this Ethernet link.  If they do not, then the issue is elsewhere.

How are you running the speed tests on the Debian machine?  Using a browser app?  Have you tried downloading the CLI package and executing that to see if that changes anything?

Thanks JefferMC. I will play around with your suggestions and test. I am using waveforms bufferbloat test and speedtest.net in the browser on Debian, I will try the CLI package as well.

I'm here to chime in.  I'm pretty disgusted right now with my decision to leave my former provider.  I just got the 2G Fiber service and have the exact same experience.  The "speed test" from the equipment is very consistently ~2.4 Gb between my modem and obviously the gateway.  If it were testing "Internet" speed, there would be much more variety in the test results.  I had to upgrade my home networking equipment (Firewalla to Firewalla Gold Plus, a 2.5 Gb switch and a 2.5 Gb ethernet adapter for one of my desktops) to the tune of about $700.  So I'm testing from a firewall with (4) 2.5 Gb ports directly to the modem with no other devices connected.  Never gets above about 700M, two different desktop computers, plugged in either through the firewall, or directly to the modem via Cat6 ethernet cable and tested again with a laptop.  All of my speed tests max out at the 1G range, but very often in the 200-300 range.  My firewall does a test every night at 3:00 a.m. and gets consistent 700-800 results in both directions.  Not only is my circuit clearly not provisioned correctly, even the 1G that I'm getting tanks constantly.  All of my streaming services buffer during the day intermittently.  Every phone call with AT&T results in the same questions on repeat.  Last Friday a technician was at my house for 5 hours (even though I was pretty clear with the phone support for an hour that it had to be in the back office because the gateway test was fine, so it couldn't be at my house).  After 5 hours of cleaning the fiber, cleaning the fiber, replacing the fiber, replacing the SPF, replacing the modem, trying new cables and about 90 minutes of them trying to convince me it was something bad on my computer, they finally agreed that it had to be with the account provisioning.  On Sunday AT&T called back because of the escalated ticket.  Once I explained the exhaustive troubleshooting that had already taken place he said "I'll call you back in a little bit."  That was 3 days ago.  There is no way on the AT&T site for me to check the status of my open "escalated" ticket.

My frustration level is pretty high at the moment.  If anyone knows a path to resolution that doesn't involve calling Tier 1 support again, I'd be grateful.  I also need to find out how to get my bill adjusted, I'm not getting what I'm paying for.

The SpeedTest from the Gateway is designed to measure the speed of the fiber link and not much else.  And if it's coming back 2.4 Gbps, that tells me that your fibers are fine.  I'm not sure what else the problem might be, but it would seem it's not there.  I'd also say, IMHO, that it means your circuit is properly provisioned, or you wouldn't be getting the 2.4 Gbps.  So, take that for what it's worth.

Make sure that AT&T Internet Security is off.  If you have Profiles turned on, you should probably turn them off, too.  And do a Factory Reset of the Gateway, just to make sure it doesn't have any funky NVRAM settings in there.  Yes, I am serious, and, yes it can make a difference in some things (not usually performance, but hey, Factory Reset is normally pretty painless unless you do an awful lot of port forwarding).

One of the issues that the BGW320 can have is glitchy Ethernet adapters.  Either they won't sync well, or they'll drop sync while in use.  So, the best you can do on that score is make sure that the adapters are reporting the expected Sync rate (and sounds like you're expecting 2.5 Gbps on all your links).  Probably not your problem, but everything should be elimitated.

Can you check the latency and do traceroutes to the servers you're speedtesting to (and I'm assuming you're doing multithreaded speed tests?) and ensure that they're close enough (latency is low enough) to not require excessive buffers?

Thanks for the quick reply. I have confirmed adapter link speed. We did a factory reset of the gateway while the tech was onsite and even replaced the modem. I used pingplotter to run latency tests, nothing seemed out of sorts.