If you want a more technical answer look at the following.
Chumly's thread post on MaximumPC:
The 64MB cached version is also S/ATA-6G which translates more clearly. Cache holds larger chunks of data before pushing it down the pipe for use. Since the S/ATA-6G has a fatter pipe, the larger chunks get shoved down it theoretically creating a faster combination.
And yes, the 64MB drives are 2x500 platters while the 32mb version is three platters; both with dual read/write heads per platter.
I wouldn't say more is always better, but shows more as media compiling and such becomes more prominent as an actually daily task. Regardless, it's worth investing in a 64MB S/ATA 6G drive at the time. The stuff down at the local store is probably a vanilla 1TB drive and is probably more expensive figuring in the Newegg restocking fee and taxes already paid.
Most people would find the performance of identical drives with 8 or 16 MB of cache noticeably different - more cache being faster. Going up to 32 MB is even better, but not so big a jump in performance. Going further to 64 MB cache will give a small further improvement, but not huge.
Now, SATA 6 Gb/s versus 3 Gb/s is a different story. Those speeds are the MAX data transfer speed possible along the communication link between the HDD's control board and the mobo's controller port. However, it turns out that the real performance limit is not in the communication channel - it's in the speed of mechanical components inside the hard drive. When you measure average sustained data transfer rate during normal use, even the fastest mechanical (i.e., spinning disks) HDD with max cache get up to LESS than the 3 Gb/s max of the last SATA version. So going to a SATA 6 Gb/s model does NOT get you any faster performance. This is not quite true for the new SSD's - they have no moving mechanical components, and some can get close to the 3 Gb/s rate now, and newer models coming expect to exceed that. But NO spinning drive will ever get that fast.
So, if you have a choice of SATA 3 Gb/s or SATA 6 Gb/s drives (there are fewer and fewer of the 3's being sold), don't pay more for the 6 Gb/s models, because they will not perform any faster. Of course, if there's a difference in cache size, that may still give you a small difference. Plus, there are other factors. For example, each HDD maker offers two or three drive design classes with differences in performance and expected lifetime that are real (for example, WD's Blue, Green and Black lines). The differences, however, are in design features other than cache size and communication rate.