While the X1 is not the most refined of speakers, esp when it comes to accurately reproducing delicate details, of all the cans i own, it literally sent chills down my spine when listening to something like Munch's stirring rendition of Bolero. I have an HD650 and it isnt even close.
For symphonies with timpani, string bass or brass, the X1 does a damn fine job. It is a very dynamic headphone which adds a lot punch & impact to the sound of an orchestra going full throttle - if that is important to you, consider these headphones.
And at 100DB/mW and 30 ohms impedance, these should do as well as any other full-sized can with iPod outputs.
Have you listened to the HD650 with the bottlehead crack? This combination seems to be universally loved. It would be interesting to hear thoughts on how that combo compares with the X1.