Comcast Internet Speed

So, I need to set up a new place with Comcast, and they are pushing for a higher speed than their basic offering (3MB). I don't believe this is fast enough for netflix/amazon prime to be in HD. My question is, do they really throttle their service that tightly, or could I anticipate possibly having a faster connection in the real world. I may also use this for streaming (either to a tablet or with the new new Fire TV trick).



Thoughts? Real world experience?