AFAIK it is all about latency and I currently get around 250ms - 400ms on a 384k line. From past posters on this forum I do not think a 4mb line will make a difference to the way your data is packaged and sent (Not sure as IT stuffz is not my forte at all).
Perhaps using a service like GameMax (I have never used them) will reduce your latency even further and therefore improve your DOT timing.