performance problem ... or not?

[Many details below, but my main question: Is there something I could do to constrain SL's use of my CPU, to allow more breathing room for other applications?]

I have a dual 2.7 Ghz PowerPC G5 system. I'm happy with the performance of Second Life, but sometimes I think it is surpressing the performance of other things running on my system.

I've read and heard from Lindens that Second Life can only use one of my processors. That sounds like a useful way of reserving a lot of power for other applications, but I don't see that in practice -- or I am misinterpreting the statistics. Or perhaps some system process that supports SL can run on the second processor?

Most of the time while in SL, both of my processors run at about 60 to 70%, as reported by the Activity Monitor. It is kind of hard to turn off every other application/process, but I've turned off everything I can.

The Activity Monitor shows 60 to 70% usage of both processors in the graph form. In the Processes view, the % CPU typically ranges from 80% to 105%. I don't see any other significant CPU usage (4% for Window server and 3% for Activity Monitor).

When I add a bunch of applications (and I typically run about a dozen, some hungry), I easily reach 100% on both CPUs, and sometimes the other apps seem sluggish.

One other clue: If I just start SL and don't log on -- just sit idle -- staring at the nice green hand and mountain scenery -- both CPUs go from about 1-2% each (my idle) to 45-55% each (on the graph) and about 75% in the Activity Monitor % CPU reading. Perhaps I have some underlying problem if SL takes up that much CPU even when its not doing anything?

Other programs that make very intensive use of the OPEN GL graphics do the same to the processors. If you MINIMIZE (not hide) the SL window, you'll see the CPU usage fall waaay off.