there are several more threads here about these two cans. Because I don't agree with the one mentioned above, here's my two cents.
I have W1000 for about 8 months now and indeed, they grew on me too.
A few weeks ago I had the oportunity to compare my W1000 to W5000. I listened to both in two sessions, each about half an hour. Here are my thoughts with W1000 as reference;
W5000 fit with very (too?) little grip in the head. As stated in several posts here, you may need to bend the wires. They are very comfortable though.
W5000 with the soft grip tend to isolate even less than W1000.
W5000 sound more like open cans.
Bass on W5000 goes a bit lower.
If W1000 have a hump in the lower mids, W5000 have that a bit more up the scale.
I like the sound sig of both. I wouldn't wanna sell my W1000 because I like the more intimate sound sig for small acoustic settings (folk, harpsicord, guitar). It would be nice to also own W5000 for larger, heavier music though...
If you don't have W5000 money to spare, just enjoy W1000. depending on your musical preferences, I think W5000 is just different, not better.