If you want you should probably invest in a i7-3770k or better. i7 for better performance.
Core i7 processors have larger cache (on-board memory) to help the processor deal with repetitive tasks faster. If you're editing and calculating spreadsheets, your CPU shouldn't have to reload the framework where the numbers sit. This info will sit in the cache, so when you change a number, the calculations are almost instantaneous. Larger cache sizes help with multitasking as well, since background tasks will be ready for when you switch focus to another window. On currently available desktop processors, i5 CPUs have 3MB to 6MB of L3 cache, while i7 processors have 4MB to 8MB.