Would changing supplier give me more speed?

I'm on Orange at the moment, and now they're pushing 20 meg download speeds it's got me thinking about what I get for my money.

According to my Orange account details my line should be able to provide 4 meg but I usually get 2 or less.

I've done the normal things like plugging into the master socket, going wired not wireless, dissabling the bell wire but don't get any improvements in speed.

So, I've been thinking of swapping supplier. o2 and Be both suggest I should be getting 6 meg.

Is it worth taking the plunge and trying out another company or am I likely just to end up in the same boat?

Apparently I'm 1.5km from my Kneller Hall exchange. Is that a long way?

Cheers,

Tony