I ordered a secondhand HD650 + 1.5m Zu Mobius. I thought since I want the 'best' Senn sound I might as well go for a short cable anyway, not that it will make an audible difference, but you never know...

I also have a 3.0m Cardas and a Grado extension lead (which looks to be about 14 kms long, ha-ha) so for times when I am not doing critical listening (close to the source and amp in my bedroom) I can always add length. None of my other listening zones (PC, home theatre) have headamps so it's no great loss if I'm not Zu-enabled everywhere.