Indeed you do.
I went with +6
Contact Hd-dude, he knows his stuff and can get you exactly what you'll need.
Sure, I can see that with the 12" bars.
When I did my 10" bars, I was skeptical because of all the varying info I found, so I ordered everything to be on the safe side. My bike is non-CVO, so it doesn't have the hydraulic clutch. When I ordered the magnum cable from Yaffe for the bars, it came in as the same length as the stocker. I called Yaffe and was told it's not need for the 10" bars cable. Installed it and it fit fine, not a lot of room to spare, but it's fine.
As for the wiring... they are clearly long enough, if they are slightly rerouted. I have a lot of stereo stuff going in mine, and I didn't want to add any more to the squirrel's nest, than necessary. I did the entire mod myself, so I can assure this is all firsthand info.
If I was going with any bars taller than the 10' set, I'd definitely say that everything needs to be extended.