Your Chronus MKNSSDCR120GB uses asynchronous NAND which has significantly lower performance when it is partially filled with data.
The Chronus Deluxe and MX models use the better performing synchronous NAND.
Check out the summary page at SSDs - Mushkin Enhanced where it says:
Positioned at the intersection of performance and value, Chronos SSDs provide
next-generation SSD responsiveness by utilizing asynchronous NAND Flash technology.
Say goodbye to rotational hard drive sluggishness by adding a Chronos SSD to your system today!