Good start. For now, my top 25 corresponds to the collective one. I ranked Gabriel at 14 and Akerfeldt at 19.
Regarding Wilson/Akerfeldt comapriosons: I ranked Akerfeldt not due to his growls (as impressive as they are, they donť count in my book) but because his voice has a very nice warm timbre - even though it is not particulary outstanding in terms of power and range. Wilson's voice, on the other hand, is a perfect definition of bland (which is not a criticism, this bland quality suits his music perfectly...