Anyone on 3MB can probably get 6MB
All you have to do is ring Telefonica and threaten to leave.
They will initially say it's not available in your area but then agree to switch you onto the 6MB service if you stay and also offer a much reduced monthly bill etc.
I saw a report last month which said there were losing market share.
The change normally takes place overnight and then you have 6mb
On www.speedtest.net I am now getting download 5.1mbps and upload 0.51mbps