I'd bet on balanced over single-ended any day of the week, any length.
I now use 1.5m length balanced cables between my Krell HTS2 and Krell KAV-500, and I heard a huge difference over the single-ended interconnects I had before. Not a "listen closely and you may be able to tell" difference, but a HUGE difference. Krell uses truly balanced XLR jacks, which as John will tell you, effectively requires twice the amount of circuitry.
The balanced connection will be louder, so that will seem like it sounds better. Just as DTS is louder than DD, therefore most people think DTS sounds better- if you take the time to match the levels you are most likely not going to be able to tell the difference.
The nice thing about balanced connections are: 1. the XLR connector itself is a good, solid connector 2. the signal is louder to drowned out noise 3. it also phases out noise
The way noise is canceled out is that the signal is sent across two cables, but the polarity is reversed on one of them. the cable acts an antenna of sorts picking noise and interference- the longer it is the more noise it picks up- a one meter cable with a good shield won't pick up hardly anything. But for long runs some noise will be picked up. On the receiving end of the balanced cable the polarity gets reversed back- this doubles the "good" signal while putting the noise out of polarity with itself and it then gets phased out.
It would be much easier to explain if I could draw a picture!
So in your case with top dollar components and good cables, an un-balanced connection should sound just as good.
But if you are a true audiophile, then just do what makes you feel better. That's what makes it fun!