This is quite a worthless excercise.
1. A DNG file *may* be compressed it it *may not* be. Obviously, if it is MUCH smaller than another version, then it IS compressed.
2. The PEF files of *some* models are compressed, *some others* are uncompressed but packed (which too is a compression).
3. The PEF files contain a prewiev image (beside the thumbnail), which can be of considerable size; I saw one 1.3MB large; again, this depends on the model, and of course on the actual image.
4. The DNG file always contains a thumbnail, but it *may* contain a mid-sized or a large preview as well.
5. The method of compression adopted in PEFs and in DNG is roughly the same. However, when compressing in a computer, the algorythm can be fine-tuned and produce a considerable smaller file than the in-camera compression.