1) i've tried the release, the rc, the wrong rc 1.19, and windlight.
2) switching clients seems to impose performance issues.
3) i delete the cache folder contents, NOT CLEAR from within the game, i delete it between each version and things become smoother ingame. Clearing doesn't seem to have the same effect as actually going in with windows explorer and deleting.
4) if you are using vista like me, enable hidden folders and go into your profile folder\app data and delete the secondlife folder. You will need to remake all your settings but it too seems to help.
I must say i can stay connected for a long time, though i will disconnect during a TP now and then.
The scenes can cause stuttering while they load.
I have been in long enough to see a nice memory leak where you will start getting not enough memory error messages from c++ runtime.
I am running a core 2 duo, 4gb ram, 64 bit vista, 8800gtx.