I don't think there is any 2-band-difference thing in real, there are number of people who got successful revaluation with 2 bands difference. Here we can see a successful EOR with 2.5 bands difference.And this refers not only to listening and writing 2 band score difference but any 2 band score difference sections
I had
L - 8.5
R - 7
S - 7.5
W - 6
I opted for EoR and got
L - 8.5
R - 7
S - 7.5
W - 7