There appears to be a custom OS modifier (your icon highlighter is a tiny power icon) underlying your system.
The other thing you could do is obviously make sure you update all your software to the most up to date versions, and also ensure that you have plenty of free space on your HD drive.
Yes, you've got several OS extensions (the icons at the top of your menu bar). Your Dashboard widgets are also taking up about 100MB of RAM. The HP Smart Panel is also bit of an resource hog. (most printer Smart Panels are). You may have other bits of installed but no-longer-used stuff taking up resources.
I had a terrible slow-down on a macbook, which I think I traced down to some sort of roaming wifi profile I installed when visiting a university, which ended up installing a whole bunch of other drivers and background services. Took some time to rip all that out.
You could try reinstalling your OS and only installing the apps you really really need. Do you absolutely need to know your fan speed?
Onyx can also help give a spring clean.
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As i said above,i own same model,same specs...it runs great and no issues with running sl at all!
I'm happy it all works for you. Clearly it meets your needs perfectly well. The other guys are having problems though, so let's try to sort them out.
Obviously they don't have much money to buy upgrades, so I'm suggesting what can be done for free, so that their systems run as smoothly as yours.