The Intel Core i5 2520M has a little better performance since it has newer features; however the difference is not that big so I see no real reason to upgrade.
Please double check the comparison chart that you provided; and you will notice that there is no big difference.
Here are some performance numbers (check the "Performance" tab:
As a note, the i5-2520M will not work for you if you're planning to upgrade just the processor. i5-2xxx and i5-xxx use different sockets, not compatible with each other.