Frame rates fall on moving and don't recover

Hi, I've just bought a new computer that actually runs SL at a sensible frame rate (my old one limped along at 1-3fps if I was lucky).

I've noticed that when I log in I get a high frame rate once everything is loaded, which then declines when I move. "Inertial lag" as a friend calls it makes sense, I've got to load new textures and objects as I move around.

What confuses me is that the frame rate seems not to come back up. As an example, I logged in at home and was getting 20fps. If I *walk* around it dips to about 10fps and recovers to about 13/14. If I fly it dips to about 8 and rises to about 12. If I repeat the process it gets worse and worse.

I also went on a long flight (900m from the telehub to the sim) and ended up on <1fps! Everything seemed stable, no packet loss, no pending downloads etc. I relogged to the same place and got over 40fps.

Any idea what I can do to help stop this, except stay at home?

In case it matters I'm running OS 10.4.1 on a 2.7GHz G5 mac, with and nVidia GeForce 6800, and your recommended speed tester suggests I get 2.4 megabits/second over my connection (which is about what I get elsewhere too)

I suspect (not that I actually know) that it is something to do with the way SL handles the cashe and video memory. I have noticed that once things rezz in a sim, they don't derezz when I move away from them so as you move objects are added but not removed from whatever.

Dumb question, but have you brought this to a Linden? There is just no way your computer is too slow. Lots of people play SL with lesser Windows machines than your Mac and don't have this problem.

I am on a 1 GHz iBook G4 and I get about 2-3 fps in the welcome area, about 5-6 most other places, and maybe 20 if I am really high up in the air in an empty sim.

Was it always this slow? Is it like this on the minimum Windows system? I get about 100 fps in Quake 3. Yes, I know it's not the same, but still. It's like watching a slideshow sometimes.