I was having a real speed problem with memory and parallels, specifically, when you exit a specific parallels VM, the memory is marked "inactive" and not "free". And each different virtual machine that was opened, consumed it's own individual chunk of memory that stays inactive after close. So the more virtual machines that you open and close, the more inactive memory you will have. It adds up very quickly.

As soon as the system was out of "free" memory, EVERYTHING ran like dog crap. I dont care what everyone says about "free" being the same as inactive, it is NOT the same. I "think" that when you are out of free memory, and open something new, the inactive memory is then paged. Not real sure.

My solution was to monitor my memory in activity monitor, and when I was out of green/free, I would open up terminal, and run 'purge'. (installed with developer tools). It is not ideal, use at your own risk, but I hate rebooting, so it worked for me very well.

I know this is only half related to the post, but i am mentioning because if you are going to investigate turning off paging, you should know about inactive memory and purge as well.