Not sure what to suggest now, bearing in mind your last response from Clive Selly.
It's annoying in that we know what the problem is, and know what its potential could be on another line card. It's sad that Zen have taken the easy way out. AAISP is about the only ISP I can think of now who might fight your corner... but even if you move to them they wont have the advantage of the other line and being able to compare and see the difference
btw.. just in case it wasnt clear about my musings about the PSD masks... was I wondered if for some reason those particular line cards were allocated a different set of masks that were available. Being that DSM selects masks from a range based upon your distance it would explain why it only affecs the longer lines. It's the mask that affects PCB and available bit load. If your line was shorter it would in all probability have a totally different mask and possibly not be as restrictive at certain tones. I said much earlier in this post that Openreach seem reluctant to change line cards so I doubt they would swap out the whole line card if its only affecting one (longer) line. Openreach have always paid less important on the upstream and never seem to make any guarantees about the upstream speed performance.
It's so damn annoying for you to know what it could perform better on one of the other line cards.
Few consumers have 2 lines on the DSLAM to compare with and the since the 0xd086 line card performance only affects the longer lines very, very few people would be in your situation. We all know what the solution would be, but if there are no free ports on the other line cards then its difficult. In an ideal world Openreach would swap places with a shorter line but I cant ever see them doing that
I think about your best chance of getting anything done is trying Clive Selly again.
Do you know how along you are with FTTP? Things seemed to move really quickly here once they'd started.