In which case the CPU will be far better, still not fantastic in terms on modern set ups, but a huge improvement over an E8400.
But for just basic tasks, you won't see a difference because there is nothing resource heavy enough to utilise the additional performance the i5 gives you.
Same as the "more RAM = more speed" myth. If an application only uses 4GB of RAM, and you have 8GB, upgrading to 16GB is only going to make an additional 8GB do absolutely nothing, so now you'll have 12GB of RAM doing nothing.
Just remember that to get into gaming you'll want to ensure the rest of your rig is up to the task too my friend!