One of the things that the new Second Life 1.20 release candidate viewer sports is a nifty new feature that busts some serious myths about avatar related lag. In short, by enabling the option, every avatar gets a number displayed over their heads showing how much work your PC needs to go through to render the avatar. This is the avatar rendering cost.
So far we have seen green numbers (low numbers, which are good), and red ones (high numbers, which are not so good). The amount of work that goes into rendering an avatar (now that we can easily measure it) isn't quite affected by things the way we thought it was.
A single article of clothing or a single attachment can send your avatar rendering cost through the roof. One volunteer subject we looked at had a single skirt that shot her avatar way into the red (and none of us would have expected that), but all of her complex avatars had lower costs than Ruth in that one prim skirt.
Another had a single necklace that had at least as high a rendering cost as this writer's avatar (including prim hair, rose, beating heart, prim shoes and other attachments) - even though the necklace itself was subtle, and hardly noticeable.
Here are two images - my avatar is runs around 400-500 normally. That's a comfortably low ARC (A distant avatar imposter is around 100-130 from empirical trials). The first is with full attachments, and the second with two removed. You can clearly see the drop in ARC.
The rose, while being a very high-prim attachment, actually has quite a low ARC and very little impact or lag on viewers. Removing both the heart and rose resulting in a drop of only 58 ARC.
Love 1.20 or hate it. You probably owe it to yourself to dive in and check the ARC of your common avatars, clothing and attachments.
Will we see products one day labeled like this? "Purse, scripted, 8 prims, 90ARC"