i5 21.5" iMac running SLOW

I am about ready to go ahead and toss my iMac at something. Chrome with 6 tabs, iTunes, Twitter and word open and every time I click on something I have to wait and wait. It slows down for the most random things like creating a new folder on the desktop. I have plenty of HD space, am using mavericks, and the activity monitor isn't' showing memory usage maxed out. I cringe each time I need to open a new app or do anything resource intensive, it's so bad that a lot of times it won't even respond to keyboard commands to adjust the volume or minimize a window.

I am tempted to upgrade to 16gb of memory vs the 4gb I have now but my i7 windows 7 PC with 4gb never really slows down for anything. My windows 7 PC is several orders of magnitude faster on similar hardware.

I the iMac 5400 rpm HD to blame? I'm ready to walk away from Macs entirely if I have to keep dealing with this garbage.