Solution : https://service.sap.com/sap/support/notes/865366 (SAP Service marketplace login required)
Key words : 
considerably reduced runtime, terms br tools, large partitioned tables, <standard sample size> 2, partitioned tables, sample size, dbms_stats package, oracle 10g, granularity partition, granularity => partition
Related Notes : 
       
| 849483 | Corrections for BR*Tools Version 7.00 | 
| 744483 | Changes in collection of statistics in BRCONNECT 6.40 | 
| 680046 | Corrections in BR*Tools Version 6.40 |