The second SSD probably has better* firmware or flash or both. It's basically maxing out the SATA II bus no matter what you throw at it.
* By "better" I mean it performs better in the benchmarks you used. A firmware that wins benchmarks often doesn't do correspondingly well in the real world. For example, Intel's SSDs are sub-par in sequential read/write benchmarks, but they perform much better in most application benchmarks.
