OS X lion and SSD

Solution 1:

Your SSD's link speed is limited by the troughput of the SATA interface and the protocol overhead.

• SATA 3 (6 Gbit/s): max. 600MB/s
• SATA 2 (3 Gbit/s): max. 300MB/s
• SATA 1 (1.5 Gbit/s): max. 150MB/s

A document by the Serial ATA International Organisation says:

What’s the real-world data transfer rate of SATA 6Gb/s?

Answer:
The realizable transfer rate across a 6Gb/s SATA link depends on the efficiency of the controller design on both the host and device sides of the interconnect. The SATA 6Gb/s interface transmits information at 600MB/s, however not all 600MB/s are realized as the user data payload because the protocol includes other data and handshaking communications between the host and device. In general, the SATA interface is very efficient. Realized transfer rates are typically very close to the theoretical maximum, which is one of the primary benefits of SATA technology for mass storage devices.

What overhead brings the 6Gb/s transfer rate down to the real-world throughput?

Answer:
There are two general categories of overhead that come into play: a communication used to send commands and receive status, and a low-level communication that handles handshakes between the host and the devices to assure the integrity of the transmission.

It's best to compare your throughput rates with that of other Crucial M4 users. An optimal comparison would compare disks using the same firmware, benchmark tool and SATA interface.

However, the best comparison I found is a thread on forum.crucial.com. In this thread users are comparing Crucial M4 128GB (firmware 009) speeds on a SATA 2 interface. Even though you are using a different firmware, the results should be somewhat comparable because the firmware update 0309 was not aimed improving transfer rates. Judging by this thread, I'd say that your throughput is fine.

The only way to get the promised speed of the Crucial M4 is by using a SATA 3 interface. In my MBP I'm currently using a Crucial M4 128GB (firmware 0309) with a SATA 3 interface. The Black Magic Speed Test gives me:

• max. 510 MB/s read
• max. 190 MB/s write

Solution 2:

You take a large hit running on an SATA2 rather than SATA3 connection. Taking a quick look at Anandtech's review of the M4, your numbers don't look out of line.

http://www.anandtech.com/show/4253/the-crucial-m4-micron-c400-ssd-review/3

The only easier way to make things snappier is to upgrade to a larger drive.

You need to be aware of performance over time. Since TRIM is not running, you are depending on the drive's garbage collection to maintain performance. There are ways to implement TRIM on Lion for non-Apple SSD drives but reviews are mixed. No idea how effective GC is on the M4 when using it with OS X.