I would think something along the lines of the Kinsey Scale

0 –
1 –
2 – Dave Matthews Band, etc
3 – Abba, Queen, Tori Amos, Willie Nelson (ever since he put out that cowboys frequently song), etc
4 – Sound of Music, etc
5 – Scissor Sisters, etc.
6 –
X – David Bowie in the 70s/80s

Problem is when you start mixing and matching. Then it skews the whole thing.

Help fill in the rest.