V6 suitable for DJing? Very.
I haven't tried the HD25, but my roommate has a pair of the famous V700DJ standard. So I'll compare with that.
Isolation is very good, on par with the V700DJ. They clamp very good for one-side monitoring too. You have to be careful when you put them around your neck: the drivers have a tendency to choke you.
You have to make sure you point them toward the front. They are built solid and they won't break easily.
The only problem I can foresee is the pads wearing down. My DJ friend used a pair of V500DJ with similar pleather pads, and they wore down in about 6 months. The cans are still usable, but they don't look as good. You could buy new 7506 pads from Sony for $10, or you could get the Beyer ones for $20.
If you're thinking about getting a pair of V6 for DJing, please do it! They're excellent for that purpose and they are an awesome value.
(BTW, on the Global Underground "Transmission" DVD, you can see DJ superstar Nick Warren using a pair of V6. I think they're a safe bet)