Someone asked me this yesterday in pm so I'll just paste what I thought about the two.
Just like the Sr200 with hp1000, the 325/hp1000 sounds similar to the HP2s but definitely not as good as the HP2s. The bass seems a little loose and heavy compared to the HP2s. Surprisingly, the bass quantity and signature of the 325/hp1000 sort of reminded me of my previous black 325 with pink transition drivers. Could be partly due to same enclosure materials of the black 325. On the HP2s, the bass is more real and authoritive. Basically, the bass just sounds more correct or right. Futhermore, the HP2s is noticeably more natural and neutral than the 325/hp1000s. IMO, the 325/hp1000 is at most 90% of what the HP2 is capable of. It's interesting to know that the various designs and materials of different grado enclosures play quite a large part (subjectively speaking) in changing the sound of the headphones having the same drivers. I was expecting maybe 95%-98% similarities but it's not. Still great sounding pair of headphones though.
If I were someone who's looking for a pair of HP1000 headphones, I'll definitely fork out the extra $500-$600 to get the HP2s. But it's quite nice from time to time to switch headphones and get a taste of a slightly different HP1000 flavour.