. . . So there you have it. The results of the 4 tests were quite surprising for me. It would seem that none of the four methods had any real effect on grain size, clustering or sharpness. However they (to my eyes), fall into two distinct groups as far as contrast is concerned. Both the standard 1:25 and 1:100 appear to make similar images, maybe a factor of wildly different dilutions but offset by wildly different times. The same could be said of the salt solutions, however the longer period of the 1:100 Salt seems to effect the longevity of the salt itself?
So in summary and based on pixel peeping only at the moment, my money is on the 1:100 Salt.
I've also done a video of this test process and will be uploading it to my Youtube channel and will put the link on this thread when ready. I will also be posting the test on my Blog at www.streetphotographyblog.co.uk