I left Pipex and a shaky 1.8mbps downlink, for UKFSN and a rock-stable 3.2mbps on Max. I'm a long way from the exchange.
The rural hideyhole happens to be about 50 yards from the exchange (a very small brick building on the edge of a field nearby) and that's settled down to a very nice 6.something.
Agree the recommendation to leave it well alone, and switched on all the time.