Group Lag

anyone experience this ?
for example:
you subscribe to a popular group with about 14,500 members.
the group chat window opens upon a message being recieved from a member sending it.
the SL client immediately slows to a crawl (FPS drops below 10, CPU useage climbs sharply).
if you switch to another chat tab window or close the group chat, the lag disappears (group voice not initiated).
it seems i have experienced this fault to a minimal degree on some heavily populated groups, but this group takes the cake.
if group voice is initiated and accepted on this heavily populated group, i might as well "end task" SL afterwards.
while it could very well be the version of the client i am using [Second Life (Dale's Unofficial Viewer) 1.18.4 (2) Rev. 416 Dec 3 2007 05:52:02 (Dale Glass Release)], i am curious if anyone else might be experiencing this issue on different viewers/versions.
thanks.

Everything Group related and Conferences have been haveing problems.. I will assume are from people spamming Chain Letters and then the sea of replies that follow.. then the hours of discussion.

This however has not been effecting the rest of the client that I have noticed ( just because I recieve a Group IM doesn't mean my lag is effected directly by this). So perhaps what you are useing tries to put Group and Conference before the rest of the Client.