The average is meaningless if your maximum value exceeds a limit.
2. What type of index is the best suited for this type of data?.
And what type of data exactly are we talking about. "TEXT" is not a useful answer.
If the raw data is too large no index is going to be "best" - as the hint suggests you either need to drop the idea of indexing the column altogether or apply some function to the raw data and then index the result.