This is just a quick note for anyone using the most wonderful Crucial C300 on OS X.
If in the “System Profiler” (now renamed to the more apt “System Information” in OS X 10.7 Lion), you see:
Link Speed: 3 Gigabit
Negotiated Link Speed: 1.5 Gigabit
And are wondering where your remaining 1.5 (or 4.5 if you have a 6 Gbps SATA controller) gigabits went, then you need to upgrade the C300 to the latest firmware. This appears to be an issue with the 0002 firmware that is resolved in 0006. Unfortunately, this does not seem to make OS X 10.7 aware that the C300 supports TRIM.
Also a tip: if after upgrading to revision 0006, your OS X will hang at boot, re-run the upgrade. It won’t actually upgrade it again (and will finish instantly), but it appears to fix something important.