Illustrator Scripting :: How To Speed Up JavaScript Looping Through All Path Items

I have a very simple javascript for Illustrator that is intended to render all filled objects semi-transparent. It works nicely but for large documents with many objects this takes ages, even beyond the time it would take to do it manually.
 
I'm wondering if there is any way to improve this script so it works in a reasonable time for large files? I'm running Illustrator CS5 on a Windows 7 64-bit Intel Quadcore i5-2400 @ 3.10 GHz System with 12 GB of RAM and an AMD Radeon HD 6350 graphics. Would upgrading to CS6 significantly improve the speed? CPU load is only at 25%, but I guess javascript cannot be run in multiple threads with the Illustrator engine? Is there another scripting language that would allow me faster processing of that task in illustrator or is my code just poorly optimized?

with (app.activeDocument) {
if (pathItems.length > 0)
{
for (var g = 0 ; g < pathItems.length; g++)
{
if (pathItems[g].filled == true)
{
pathItems[g].opacity = 50;
}
}
}
}