Whilst I know you'll probably dismiss this answerto your problem , I figure I'd suggest it anyways. Why not have your computer reboot itself very eraly in the morning or whenever you're sleeping? I was having similar issues with one of my systems and I simply set it to shut down at 4:30am and start back up at 4:45am... It helped alleviate most of the slowdown and memory problems with the machine. Though I wasn't running with that amount of free space... as everyone is suggesting you should really keep more space available. I always try to leave 20% of my drive available at all times...