So I went ahead and done this earlier this morning (it was quite cold!), I used pre-crimped earth cables from halfords as I'd won £40 vouchers from work so why not use them! They're also 8awg.
For my A3 I did Throttle body lower mount screw to centre point which in this case is as Tufftys guide, the point where the engine hoist hook is mounted, it's an Allen bolt.
The rest were from coil pack earth to centre point, auto gearbox to centre point, centre point to battery negative and finally chassis to battery negative using the passenger wing mounting point.
Did it make a difference?
Definitely. The car revs are a Lot more stable on cold start up, like rock solid at each rpm pretty much. The throttle is more responsive, Idle is now smooth as my Mercedes, sticking at 700-705 now, was not ranging from 695-710, and also as an unexpected side effect, the headlights are brighter and the auto gearbox changes have also smoothed out.
Worth whole mod tbh, and only cost me £21 which in my case was paid for by work lol.
Thank you
@<tuffty/> and the original post owner too. I'll upload pics of mine in a bit.
well just to rub it in Im a sparky and I got mine for free 
