First, sentiment is reality. Remember the animal spirits of Keynes. Greenspan also said that if he could figure out when greed turns to fear, he wouldn't need any other model.
Second, the 8% growth rate of 2003-08 for India was during the years of the global credit bubble. I would not be wrong to simply lop off 2%-3% off that to come to a trend GDP growth of 5%-6%.
And since in FY10 we will go below trendline growth, I would bet on a GDP growth rate of 3%-4%. Even agriculture growth can be negative depending on where agri commodities prices move. So far, I have seen only a few brokerages such as GS or Macquarie talk of 5.5%-6% growth in FY10. This to me is the top end of the trendline growth of 5%-6%, not the bottom end of trendline growth of 8%.