My move to Newnet's base package turned out to be a false economy and they wanted £12 to upgrade me so I decided to head back to Zen.
All new connections are ordered as ADSL2+ and you have to request a regrade back to the ADSL Max equivalent product.
My connection has been stable now for 20 hours following migration and am getting 1.4 with a 61 dB attenuation.
If this keeps up and if I find I go over my 10 GB cap I might look at IDNet again