Well i migrated to Vivaciti on the 8th from Enta after their throttling shenanigins and what a difference,admittedly i am now on LLU (75GB package via Tiscali tail)but speed is constant 24/7 so far,will report again in a month.
Had a few doubts about a service using anything to do with T but shouldnt have, Vivaciti run all the main connection.
http://www.speedtest.bbmax.co.uk/results.php?t=1260546680&v=8678313

Support has been good when needed via their own forum,pre-sale enquiries answered in good time and after sales queries sorted as well.
Give them a try especially if LLU options are limited.(no Be/o2 sky for me)
Also worh noting that the LLU showed as unavailable to me after previously saying it was,a message to Vivaciti sorted this and migration down time was around 20 minutes.