Cache is pretty much the least important thing to consider when buying a hard drive. If a drive has too little cache it will affect performance, but once you get to a certain level adding more cache doesn't make much of a difference - and all of the drive manufacturers include enough cache to optimize the performance of their drives.
What's much more important is the access time and transfer rate of the drive.
32MB is the best cache for HDD but 64MB is not needed as it does not increase performance or help anything... Cache is just to make your programs start up faster but the loading will be the same... Cache just store where the file is and instead of it searching for it, it already know where the file's at so it just go straight there and get it to open...
It was indicated that programs will load quicker but I'm not sure that's true. A hard drive will copy an accessed file to the faster cache (when accessed) and then when the hard drive is queried for a file it checks the FASTER cache first.
Here's how a program loads (from fresh boot):
1. Start program (i.e. Microsoft Word)
2. Main elements copied from hard drive to System RAM
3. program RUNS from System RAM
If we CLOSE the program, it will actually stay in our System RAM if we have enough, thus starting far quicker.
So the amount of System RAM has a HUGE impact on how quickly we can restart programs.
The bottom line is that in a modern system with sufficient RAM it's difficult to find scenarios where the hard drive cache size makes a big difference.
*Also remember that a LARGER CACHE on the hard drive can actually slow your system down since it checks this cache first to see if the file is there, so it's slightly SLOWER if the file is NOT there but FAR FASTER if it is.