You're aware that if you use FTTC again exactly the same thing will happen with the new ISP and they'll be completely unable to do anything to improve your latency, right?
If you need an ISP that has end to end control to ensure your latency isn't increased by line management your only option is to take an LLU service. Sky interleave and run line management, Be and O2 are going to be assimilated into Sky's packages in the not too distant future, your options are a service that resells TalkTalk Business or one that resells Cable and Wireless.
just thought an update was in order been on skys ulimited fttc service almost a year had 1 issue in that time where engineer disconnected me in error resolved with a single call, for the record heres my ping to bbc.co.uk btw ping to NL server is 20ms uk servers is 16ms or less, couldnt be happier with the service
C:\Users\Css>ping bbc.co.uk
Pinging bbc.co.uk [212.58.246.104] with 32 bytes of data:
Reply from 212.58.246.104: bytes=32 time=13ms TTL=57
Reply from 212.58.246.104: bytes=32 time=14ms TTL=57
Reply from 212.58.246.104: bytes=32 time=13ms TTL=57
Reply from 212.58.246.104: bytes=32 time=13ms TTL=57
Ping statistics for 212.58.246.104:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 13ms, Maximum = 14ms, Average = 13ms
hopefully Zen will one day return to being as good as they once were