This blog post from Nalates Urriah gives some instructions on various settings you can tweak/change to try and improve your viewer’s performance, especially at events where are there are lots of avatars present.
I used to use the Ctrl+Alt+Shift+4 to derender avatars at busy events. However, I found it that sometimes derendered other things that weren’t avatars (like certain machines at The Arcade). I’m not sure why it does that, but I have since just derendered avatars using the radar tool in Firestorm.
Some interesting information, but tweak/change with care. 😀
Source: Second Life: Render Speed Tricks | Nalates’ Things & StuffNalates’ Things & Stuff
A Kat and A Mouse 