Below are the stats I used to compare my program to ECM's. A normal cd image contains more than 100,000 sectors. I first compared different sectors.

Note: COSI size is based on total size of both files.

1 Sector (CRC is remakeable)

Original Size:2,352 bytes
ECM Compression:2,083 bytes
COSI Compression:2,053 bytes

1 Sector (CRC is non-remakeable)

Original Size:2,352 bytes
ECM Compression:2,367 bytes
COSI Compression:2,333 bytes

The next tests are done on actual psx cd images, which will probably be the main use of this program.

Final Fantasy Origins

Original Size:249,681,264 bytes
ECM Compression:221,169,453 bytes
COSI Compression:219,364,757 bytes

Panzer Bandit

Original Size:284,624,928 bytes
ECM Compression:266,696,032 bytes
COSI Compression:235,666,470 bytes

As you can see, COSI's compression will always be better than ECM's (sometimes slightly and other times dramatically depending on the image).

Note: All the images tested on were able to be decompressed and matched the originals 100%.