Quick question

By sandbox games do you mean browser based flash games?

I am pretty sure flash games can only ever use 1 core, so the only thing that matters is having the uberest per core statistics you can get.

If I am right, the core 2 quad @ 2.83 ghz would probably be worse than the core 2 duo @ 3.0 ghz. The other core could easily handle the computer's regular tasks and it certainly doesn't need 3 cores for the other regular tasks nor would the extra 2 cores benefit it in any way.

I am pretty sure that this is inherent to Flash and not something you can really address easily.

If you are talking about something other than Flash programs, the problem could be elsewhere.

There's not too much difference in gaming power between the two processors. While the Q9550 is slightly better at gaming, you probably wouldn't notice the difference.
http://www.tomshardware.com/reviews/gaming-cpu-review-overclock,3106-5.html

You may try cleaning your system of resource wasting crap and registry errors to take some load off the processor and speed up your gaming. I use CCleaner regulary. Do the Clean and Registry both.
http://www.piriform.com/ccleaner