GHz is a great measurement within the same family. For example if I have an Intel® Core™ i5 at 3.1GHz vs an Intel Core i5 3.3GHz. it is clear that the 3.3 is the faster one. Cache is memory on the processor and since it is faster the system memory it does help the processor run faster. There have been some old proessors like the Intel Core 2 Duo E6300 and Intel Core 2 Duo E6320 which only had 2MB of additional cache, in cases like this the 2MB of additional cache did add some additional performance on some applications but it wasn't large and it wasn't on all applications.