My thoughts below are listening to my setup with Yamamoto HA-02 amp, Benchmark DAC and Denon SACD player as source.
W5000 is sweet sounding with very good instrument separation and sound stage. The bass goes very low, is textured and detailed, but lacks punch like Sennheiser HD 650. Treble and female vocals are the key strengths of this phone. The W1000x has a smaller sound stage with smoother sound, has better vocals with male singers and has more bass quantity.
They sound different enough for me to own both, though if I were forced to keep one, it would be the W5000 currently. My impressions may change once the W1000x burns in completely as I have used it only for about 30-40 hours so far.
I love the AT sound signature and can listen for hours without any discomfort or fatigue. Many times, I prefer to listen to my AT rig over Stax. Thats why I am so tempted towards investing in one more if it sounds different.