I recently picked up a pair of W1000s and they're certainly the most detailed cans that I own. I can only imagine how much better the 5ks are. But they're a bit thin and light on the bass. Most negative comments on them will say that. And that's what my listening told me--they shined on a few songs, here and there, but overall they didn't impress me.
And then I found the Fitz mod thread and made a F1001. It's really easy, only took me about 40 minutes. And like Strangelove said about the F5005, the mod totally changes the signature of the cans. They're now, more or less, fantastic. The comments that describe the F5005 seem to fit the F1001.
I went from thinking of selling the W1000s to getting upgraditis for the W5k, so I could make a F5005. Although, in the mod thread I think one user mentioned there not being that big of a difference between the F1001 and the F5005. I can't comment on that directly, yet, but if it is true then the F1001 is a an even better value than I think it is.