Quick back story... I live in the sticks and only have WildBlue satellite internet available (1.5mbps and 17GB/month at an ungodly cost), other than mobile broadband options. I'm looking for something faster, and with a larger/unlimited monthly limit for activities such as light XBox Live gaming, Netflix, and Skype.
Although the plans say 'Unlimited' 4G, the asterisk indicates 4G speeds up to 5GB/Month. That said, the footnote specifies 2G speeds for the remainder of the month if there is overage on the 5GB limit. I expect to exceed that monthly limit regularly, and by a significant amount.
The information you found is on the money. Throttled EDGE speeds can range quite a bit. Check out Data speed reduction to get a better idea of what to expect. You may also find this discussion helpful.