Cables do not change sound that drastically if anything. Parts around the driver? The SR125 and SR60 both use plastic, what other parts are you looking at?
Agreed...I've owned the following Grados:
SR60
SR80
SR125
SR225i
SR325is
RS1
RS1i
And they were all quite different, way more than just the subtle changes that a cable can make....sorry, but I don't this that the same driver argument doesn't apply.