That's the thing I like about Crucial, they tend not to inflate their numbers and typically undersell. Like with my Lexar (Crucial) Triton USB 3.0 flash drive 180 MB/s instead of the advertised 150.
Even with the M4, read speeds up to 500 MB/s, but it exceeds it. Writes up to 175, but it exceeds it. OCZ on other hand rarely meets their advertised speeds.