Original chip E5400. Lets say you didn't have to pay for an upgrade to C2D E8200 or E7500... I know the E8200 is older than the E7500, but what which one would outperform and why would you choose one over the other? Would it even be worth opening the case?
It's a toss really. The E8200 has more cache but the E7500 has a faster clockspeed. Overall they are very close but sometimes cache will be slightly better and sometimes core speed would be slightly better. http://www.anandtech.com/bench/Product/58?vs=87
I would go with the E7500 if you have no intention of overclocking. The higher clockspeed will benefit you more in general.
Is it worth the upgrade? Depends on 3 things:
1. What you do with your computer
2. What kind of computer person/enthusiast you might be
3. Well, there isn't a 3rd thing but I wanted to make a list. And a list is kinda pointless with only two items
As an example, I am an avid computer nerd. I enjoy everything from upgrading to overclocking and even reinstalling windows at least 5 times a year. I would crack open my case to upgrade to my overclocked Athlon IIx4 620 to an Athlon IIx4 630 if I got it for free and try to overclock it too. Even though I will make no use of the extra power.
Which brings me to my first point, what you do with your computer. If you do things that are time limited and use 100% CPU time, such as encoding, video editing or similar, a free upgrade would make things faster by a few seconds to a few minutes depending on total time expected.
If you fall into this category though:
-I don't want to open my case unless I really have to
-I surf the net, do email and play games that only use 1-2 cores with my low end 4670 and I don't do time limited things
Then there is no need for the upgrade, if you really don't want to open your case.