Cache is like a small chunk of very fast RAM right next to the CPU. Size of the cache doesnt matter as much as how it is laid out. Larger cache is slower for the system to access so if its large but laid out poorly it wont improve performance any more than a small but well laid out cache.
If 2 CPUs are from a same family and the main difference between them is cache, then you won't see a noticeable difference between them in almost all tasks.some few apps such as very CPU-intensive tasks benefit from more cache. In games,however there isn't much of a difference