As regards track differences - I've run the figures on NSW races using the SP to find the favorite or longest priced horse and the returns based on the NSW TAB payout.

Longest priced horses return.

• about 56% of your cash with a strike rate of 2.33% on heavy tracks.
• about 53% of your cash with a strike rate of 1.51% on slow tracks.
• about 41% of your cash with a strike rate of 1.08% on dead tracks.
  
• about 42% of your cash with a strike rate of 1.13% on good tracks.
  
  

Favorites return.

• 88.02% of your cash with a strike rate of 31.18% on heavy tracks
  
• 89.77% of your cash with a strike rate of 31.89% on slow tracks
  
• 89.37% of your cash with a strike rate of 32.76% on dead tracks
  
• 90.23% of your cash with a strike rate of 33.83% on good tracks
  

Not a great difference with favorites but the longshots seem to do better on worse tracks.

KV