I only asked because I came across the b) pronunciations on an online dictionary. I have never heard them myself in my 8 years in the UK. I thought it might have been because the pronunciation was too subtle for my non-native ear to pick up.
Here are the phonetic transcripts I came across:
superman ˈsjuːpəmæn superbsjuːˈpɜːb
Super with the yod /j/ is more likely than Susan with the yod. Even so, it is in the minority.
I think there is a comment about the pronunciation of Susan in Hardy's Mayor of Casterbridge (1886) which suggested at that time Susa with the yod was considered normal. I have so far been unable to track down the relevant sentence.