What is bottlenecking my system the most?

WindyDayEveryDay

Honorable
Nov 19, 2012
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I understand that my system is limited by some hardware components, probably the graphics card the most.
I am considering an upgrade on one or two of these components, but I'm not sure which one will result in the most balanced system.
These are my current components:
-Intel i7 860 (Lynnfield)
-Gigabyte P55-USB3 Motherboard
-Nvidia GeForce GT 240
-WD Caviar Green 500GB (I have an external HDD so storage SPACE is not an issue)
-2x2GB Kingston DDR3 RAM
-Huntkey 550W PSU

I was considering upgrading either the...
HDD to the Intel 520 series SSD (keeping HDD for storage)
OR
Graphics card to Nvidia GTX560Ti
...or are there better options? I play games casually and experience slightly more frustration with the horrendously long load times (even after defragmentation) than in-game graphics detail. In other words, I play games like HoN and SC2 where I believe the in-game graphics lag (or mostly lack thereof) is not an issue, but I also sometimes play MMORPG/FPS where in-game graphics seems to be more of an issue. Advice please?