Great question. When you hit the data speed reduction threshold on your Mobile Broadband device, the internet speeds are reduced to 100 kbps, which is twice the speed of a dial-up connection and about the same speed as EDGE.
Hope this helps!
It'd definitely true that you can get faster speeds on the EDGE network, depending on a variety of factors such as signal and tower load. This can also go the other way, where I live EDGE speeds are around 40-50 kbps. When you look at the network as a whole, the typical EDGE speed someone will get is about 100 kbps.