Ooh. Response from the big man himself. Maybe there's hope of actually getting this resolved. Feels a little bit like talking to...maybe not quite god... let's go with gandalf. And I never really left testmy.net. Been visiting at least weekly to test ever since I signed up. Just neglected to sign in. >.< Anywho, thank you for all the suggestions and reading material. Unfortunately, there wasn't much of that I wasn't already familiar with or hadn't previously poured through. So let me shine a little more light on the issue.
First off, I'm a mac user. (*le gasp!*) While a windows machine is accessible if necessary, I can say this problem affects all machines on my network regardless of OS. Even Linux which does tend to pull down faster downloads (~80KB/s +) sees this issue.
Now for the details. This has been an issue for about two years. I am on AT&T's 6 mbps plan. Most days the modem claims it's a little faster. Best days I can see speeds hovering around 810 KB/s. These were not so rare for a short period. However, as of late my network condition seems to have declined for whatever reason and this problem has gotten worse.
I've tried various setups. Nothing really makes a difference. Currently I have my motorola 2210 modem set to bridge mode, with an apple airport extreme handling the pppoe. But, even with ethernet cable plugged straight from my computer into the modem and the modem handling pppoe, this issue has presented itself.
It's not just a TestMy.net issue either. It affects my results on Speedtest.net as well. Testing on my laptop doesn't visualize it so well. But my iPhone does provide an interesting little graph of what's going on.
I used to think it was my router since the problem seemed to be, although present on ethernet connection, worse over wifi. But three different routers later and it's still there. And like I said earlier, wired directly to the modem it still happens.
Now about that MTU. I'm truly hoping my apple router automatically figures that one out because it certainly does not have an option to change it unless I along with most of the rest of the internet have been oblivious to something. I have changed it on my computer and nothing really changed. Also with previous netgear and linksys routers I have manually set it in both stock and ddwrt firmwares and while it made me feel better, nothing really changed. If I remember correctly, ddwrt actually defaulted max mtu at 1492 for pppoe.
I feel like there were other details I wanted to include, but those are lost in a world of other thoughts right now. Let me set aside a small amount of modesty for a moment and say that I tend to have a great deal of skill for diagnosing and finding a solution to an issue even when I may not initially have a complete expertise in relation to the issue. But this has baffled me. I don't understand why every device in my house seems to have to ramp up in the first few seconds of a download to reach that peak speed. All the same devices on other networks will easily perform at the max of that network's download capabilities. The speed is there. It's apparent when the download gets stable. But I don't know what's wrong there at the beginning and lately it's made my web performance absolutely terrible. Page loading is far from snappy.