Orange to Sky?

Hi people, been with Orange for about I year now and wondering whether to switch. Got my eye on Sky as they seem to have reasonaly good reviews and according to DSL Zone their LLU is available at my exchange.
What I really want is more speed though. Trouble is I'm about 4k from the exchange as the crow flys and my stats are lousy.

Noise Margin 11.6db
Attenuation 61db
Attainable down 1536k

Down 1376k
Up 448

Interleaving on

Master socket stats are pretty much the same

I appreciate I'm never going to get 8Mb on this but for the first few months I was consistently getting higher syncs and nearly 2Mb down, this has fallen off in the last few months (both synch and speed) to about 1Mb. I know its rate adaptive but at no speed have I had any connection issues. At the higher speeds the noise margin was at about 6db - is there anyway to force this?

So the questions are:

can I eke any more power out of my livebox orange setup?
am I going to see any appreciable benefits from moving to another supplier?

All advice appreciated

Jim