one thing is that the black magic benchmark uses uncompressed data. The speeds advertized are using compressed data. Xbench is a benchmark tool that uses compressed data.
That said your macbook is from 09. It may be using the older nvidia SATA chipset that has compatibility issues with these ssds. At the top of the system info screen see what your negotiated SATA link is. it should show your chipset and negotiated SATA link speed. The older SATA chipsets really are not capable of faster transfer speed.
