OK TLDR: I succeeded in rescuing the disc!
ddrescue zoomed through the remaining 1100 or so Kb on the last attempt a couple of days ago so I thought "Wow!". I ran through the remaining steps and unfortunately makemkv was still unable to rip the titles I needed from this one so I gave up temporarily.
The isopropyl didnt seem to make any difference but I will still use it to clean any discs that I have trouble with later.
My suspicion is that the drive didn't kick up a read error but instead gave garbage data (hence the ton of hash check errors in makemkv?), I kicked myself for not making a backup of the mapfile before I ran that last rescue.
For my linux machine I had actually installed ddrescue-gui so I ran that up with the intention of doing another rescue attempt (from the start), I noticed several presets in the settings..one of which reduced the block read size and was labelled "best recovery" so I ran the disc up with that setting and the whole disc was rescued in just under 40m!?!?! (the previous rescue would take ~16hr).
The next step I took was out of necessity rather than anything else, I am running out of HDD space so instead of copying over the BDMV folder to the location of the .dat file I placed soft links to the three top level folders in the mounted disc image (the image just freshly rescued) so I didnt take up the space.
I ran up makemkv via the dat file and VOILA!!!
Needless to say im a happy chappy, apologies for the thread hijack but I assume this info will be useful for someone down the line, I will be backing the rescue image, dat file and everything else somewhere safe should I need it again!
I have another disc I haven't been able to rip for ages so I will attempt the same process with that one.