I think outdoor HC which is played in 50% of events can easily be divided into fast and slow HC. Slow hardcourt with long painful rallies while the summer hardcourt tournaments with less rallies and more attacking tennis.
Nole - outdoor slow HC, outdoor fast HC, clay, indoor, grass,
Rafa - Clay, grass, outdoor slow HC, outdoor fast HC indoor
Roger - Indoor, outdoor fast HC, grass, clay, outdoor slow HC
Andy - Outdoor slow HC, indoor, outdoor fast HC, grass, clay
I was thinking about the same - fast to slow HC, but how i wrote in my first post, indoor-outdoor difference is i think bigger and it is clear, but by slow-fast HC it is not always clear, where is medium and so on
But definitely we can divide 3 surfaces to 5 different, because clearly difference between slowest HC to fastest HC is far far bigger than from slowest clay to fastest clay for example. Also indoor- outdoor conditions are totally different. Rafa is nice example, he is generally i think good on HC, but not indoor HC.