Crucial promised a 17% performance increase in the Crucial m4 over the C300. The results showed that they delivered on that promise, showing 17% gains in sequential read speed and 19% gains in write speed.
The drive seems to be designed to perform decently in lighter workloads, such as average desktop usage. The drive will provide you sequential read and write speeds that match the figures quoted by Crucial, although the latest SandForce-based SSDs have an edge here.
On the other hand, Crucial's solution excels when it comes to dealing with incompressible data and delivers great 4KB random write performance. Generally, the drive seems to perform very well with 4k data than with larger files, where solutions such as OCZ's Agility 3 and Vertex 3 SSDs are faster.
If you are dealing with demanding tasks that require high IOPs, you 'd better look for other SSDs as the m4 256GB cannot reach the competition's performance levels.
Crucial has an ace up its sleeve, and that's price. The m4 is priced well below the SandForce drives. The 256GB version is currently available online for $420 (version with no backup software included) while for the retail version of the OCZ Vertex 3 240GB you will need around $500. The m4 is also generally cheaper than it's Marvell-based competition as well, giving it a pretty attractive value proposition. For example, the Intel 510 250GB is listing at $565 and the Corsair P3 256GB is listing at $450.
Typical desktop/notebook users will appreciate the m4 as it will give them the performance quoted by Crucial plus generous capacities at a very attractive price.