Well, this is going to depend, is your 75 seconds primarily due to processing on the SQL server or is it primarily due to network transfer of data? If it is due to network, then grouping should be faster assuming that you do not have a ton of different groupings since you are trading a single query for potentially 4-8 queries, one per group. With a grouping query, the SQL server has to do more work calculating the end result of the query but it typically has to transfer a lot less data, potentially 4 or 5 rows versus 10's of thousands.

Have you run the report query directly on the SQL server from the Management Studio and does it take the same amount of time? Have you looked at Query Analyzer to see if there is anything you can do to improve performance?