You might be able to see a slight color difference if one of the negatives has more stain than the other. The one with more stain would look slightly browner than the one with less.
Sandy, you are absolutely right. There is a noticeable (more) brown colour on the negative with the 2:2:100 dilution. As a test once more, I just finished developing in the 1:1:100 dilution two negatives. I made a visual on all that I have done so far and it is clear that the 2:2:100 dilution results in a more brown stain.
I would like to stress how nice PYROCAT HD and Efke PL100 work together. It seem like cheating when negatives like this come too easy.