It is really down to the location of your new house in relation to the exchange, you connection type (ADSL or Fibre Optic), the contention ratio for the bandwidth allocated to your part of the exchange and the quality of the line. You can get postcide estimations
on websites like Samknows.com, which will give you an idea about what to expect in your new area.
They were at one point ranked as the worst ISP for anything, That was admitedly when they first introduced traffic management and made such a mess of it that no one had a decent cennection for anything and gaming was impossible.
That said you need to do some real research on them, look at thinkbroadband.com ask questions there it may well be and most likely is that they have sorted themselves out (If they had not they would not have a business left IMO).
However you would be unwise to take the word of one subscriber on the xbox live forums for how good the service is.
Fight me on xbox live RTCW :) you know you want to...