Hi,
Interesting...
Has the aggregates the correct/missing indexes ? are statistics up-to-date for aggregates ?
Check this SAP Note 2138611 - SYB: Better table statistics for star schema tables of an InfoCube
it is included on the last version of the BW Correction Collection.
It would be helpful to run the query using RSRT, you can debug for there to get the SQL statements involved on the report and identify which is the one causing bottleneck (if any). From there you can check the statements generated using or not the aggregates.
You can also use DBACockpit (Performance -> SQL Statements) to check which is the query having more resources consuming, you can filter by one of the table that should be accessed by your report.
Regards,
Victoria.