Hi. I'm also having problems with low and inconsistent framerates in JO. Even on 30-50 player games it can be quite bad but I don't have any problems in any other games.
I ran 3dmark 2001 and got a score of 12045
http://service.futuremark.com/compare?2k1=7828564
And 3dmark 2003 with a score of 5908
I'm not sure if its something in the demo or JO that doesn't like my system but on some occassions its barely playable. Unfortunately I cannot dynamic compare the 3dmark results becuase supposedly there aren't any to compare with
Hopefully the final game doesn't produce the same problems.
Stuart.