How are you running the report, in BIDS or deployed to a report server? I'd recommend deploying it to a report server and testing performance there. You can query the ExecutionLog3 view in the ReportServer database to find out a bit more about what part of the process needs the most tuning: data retrieval (the query), processing (calculations, etc... on the report), rendering. You can then use this data to assess if changes you have made are working and how well.