This HDD would be exclusively for the OS (Win 7 64-bit) and programs. There will be no personal data files on this HDD.
Currently, the space used for the OS and programs is about 146 GB. The HDD in use now is Seagate Barracuda ST3750525AS 750GB 7200 RPM 32MB Cache SATA 6.0Gb/s 3.5" (overkill, but it was laying around).
The smallest HDD with 6GBs is 500 GB. And if I want 64 MB Cache, then the smallest available HDD is 640 GB.
This will be used exclusively for the OS and programs. Common sense tells me that 64 MB Cache is better than 32 MB Cache, but my question is how much of a performance improvement will I see? Ignore price differences.
Even a number by the SWAG method will suffice.