Hi,

1. Query execution timing difference with or without indexes may
not be much if the tables you are joining are small (few
hundred thousand rows).

2. For joining large tables (million's of rows) you don't
need an index on any column in the where clause.

3. Multi table query will join the tables first and then
filter the rows according to the where clause. You should
not be having an index lookup for the filter.

4. Comparing the trace is the way to go.
Check the trace for query with and without indexes.