I think that throttled connections which are been manually capped by the ISP could see a vast improvement by switching, once the LLU comes into play.
However, if you are like me and generally don't suffer from heavy throttling, and the max my line can receive is 4Mbps, I don't think that switching will make a difference to speeds.
As surely, your line can only handle what it can handle, and switching will not change that?
According to KC my line can handle 17Mbps which seemed fine when some testing was done when Max was being particularly crappy. I am still on ADSL at the moment so restricted to 8Mbps. From what I read ADSL2+ isnt throttled to death like ADSL is on Karoo so yeh, you wont get throttled.
I am loathed to upgrade to ADSL2+ though now as I don't want to be tied into another contract if MS3 turn out to be half decent.
As for the line speeds, MS3 'claim' that it should be improved, but I will believe that when I see it.
Mike