01-28-2011, 02:06 PM
I would say your primary issue is not enough free space on the drive and what free space you do have is very fragmented.
You're down under 20% free space (some long time Mac users will contest my experience). But, I'm going to say if you're playing intense games that will also use a large amount of virtual memory, at 20% free space and especially on a Mac where you've never done a defrag, your virtual memory is scattered all over that drive.
I start noticing these issues myself at about 30% free space and in my past hardcore gaming days it became unbearable by 20% free space - and I contend it carries over into OS X the same as it does in Windows. Today, I attempt to maintain 40% free space on system drives of all sizes up to and including 1TB in size. I have never put an OS on anything larger than 1TB, so don't have any experience related to keeping a system running full bore vs free space on those 1.5-2TB drives.
You would probably see some improvement with a defrag, but with what you're doing - I would encourage you to free up some space. Try to get to 30-35% minimum and either run a defrag or create a bootable backup and restore your internal from the backup - this will in essence do a defrag for you.
Along with the above, if you haven't been doing any sort of maintenance, it's time to run a Repair DisK, Repair permissions and grab Onyx for some housecleaning - all these before the defrag or restoring from backup.
edit: If you have any questions about any of these steps, feel free to post back.