Well assuming zen are using WBMC shared. Then you got 2 options.
1 - wait it out, plusnet are shifting their customers onto another WBMC product, since they are by far the biggest isp using WBMC shared, then this will free up capacity and I expect congestion issues will go away, obviously I got no idea of how long it will take plusnet to move all their customers, or at least enough to stop the congestion.
2 - Ditch BTw and use a isp with their own backhaul, which is either entanet, talktalk (talktalk resellers of ttb recommended) or sky.
I think all the issues that put you off pulse8 are trivial minor one's. I would go with one of these 3.
aaisp ttb resold
pulse8 ttb resold
sky
Also its good sense to use someone else's network for the website, as if zen's network ever goes down the first thing their customers may do is look for a status update on zen's website or contact details.
Edited by Chrysalis (Thu 14-Jan-16 05:37:48)