Well, the 1TB drive will be slightly fast than the 500GB drive, but not due to the cache size. It's due to the platter size vs. data compression. More data is packed onto the same area of the platter of a 1TB than a 500GB.
Cache size really doesn't matter anymore, as the bandwidth of the drive ports (i.e. SATA II) are much faster, and don't require the drive to "hold" any information, waiting for the drive controller.