You weren't kidding, pricey stuff this flexible cable! If I ask nicely the electrical guys at my work might have an offcut of something suitable kicking around.. worth a try!

The motor didn't seem to be the issue in the end, I don't think anyway.

I was still getting the dimensional inaccuracy's when running a program so I went through the setup process again within UCCNC to define the steps/rev. This time I done it over a larger distance where as previously I just used the max travel of my DTI (only about 15mm), this time I just used the closest accurate thing I had at home (50mm slip gauge).

Running the program again, the dimensions were pretty good, 0.15mm of what was programmed, which is most likely backlash to be honest.

A few more test cuts and see what happens over larger/smaller lengths!