Goscomb are another AAISP type provider: http://www.goscomb.net/connectivity/broadband/fttc
I was looking at them for FTTC at my new house, but decided to stick with AAISP instead (as I sometimes download a lot and I can schedule that between their 2am-6am night-time special slot, effectively meaning I can download way more in a month than what Goscomb can provide for the same price, and even Zen for that matter).
Goscomb can do 120Gb/month for £36.00/month (inc VAT) but that's only on a 40/10 connection (+£4 for 80/20). Remember also, switching provider is not going to solve the underlying issue as to why interleaving is being applied on your line
- you'll be in the same situation if you switch providers.
I'm not sure if you are going to get what you want from any of these niche providers like AAISP and Goscomb. As has been said, maybe better to try one of the more "sheeple" type ones (BT/Sky). I wasn't interested in that as I do not trust the whole unlimited splurge. What I mean by that is - yes, it will be unlimited, but they'll likely traffic manage your connection where necessary, and slow it down if they need to. I'd rather manage (and pay for accordingly) my usage instead, and have a fast clean connection without any of that tampering.
If latency really is the main issue here, and you were only a few hundred yards from the exchange, I would suggest moving back to ADSL2+ on an LLU provider - you would then be able to fixate the line to fastpath and keep it that way. But I gather you went with FTTC for the speed - which unfortunately has this automated DLM shenanigans at the cabinet.
Not sure what else to suggest really.