Is your problem latency / jitter or speed, the way I see it is you've got 2 choices, well at least I have, Virgin with some peak time jitter but fantastic speed or BT with poor speed and less jitter. No idea how BT FTTP compares to Virgin, possibly less jitter and latency ? I don't have that available where I am.
The base line latency is very hard to predict, certainly it is with third party ISPs which will likely use the BT infrastruture before handing over to their core network. Having been a BT customer for many years and tried other third party ISPs I'm not impressed with the latency or jitter of Virgin but I'm willing to work around it to get the excellent speed on offer.
No idea but perhaps the hub5 will be better when it's rolled out.