I would only take the 2300 at this point if I was doing a lot of things in which I saw the benefit of having four cores rather than two and did not use things that thrived on single-thread performance. The i3 here has better single thread performance than the i5 here, which is still extremely important in gaming. For an office-type PC doing a lot in Excel or Statistica or something, I would take the i5, but I would personally keep this i3 in your situation.
The i5 wouldn't be notably *worse* than the i3 in those single-thread applications outside of benchmarks -- you won't really notice that difference in real-life -- that's not the only consideration involved. You're also moving to a platform that's a couple generations older with a motherboard that is also 3 years older.
I don't think it's really worth the trouble. If you want to upgrade your CPU, I'd look at straight CPU upgrades on current motherboard rather than going back in time.