Rather interesting results you got there, but definitely not something I've seen as normal for a DSL connection. You're getting the full amount of bandwidth coming into your line when UDP packets are used at least, though what I find off is how bumping the size up to a rate higher than your connection could sustain threw it off. Here's a test from my 1Mbps Verizon line to compare.
Here's a test from a Verizon Business connection that should be at 1.5Mbps, but is only running slightly above 1Mbps due to that "optimization" nonsense. I ran this over a VNC connection so the results are slightly skewed.
For now until we find out what is going on, I would have to leave it with congestion at the moment.