There’s a new (June 27) benchmark for SAP-SD, three-tier Internet configuration. See more here:
The benchmark used SQL Server 2005 (64bit) on Windows Server 2003 Enterprise x64 Edition, running on an HP ProLiant DL585 (4-way, SMP, dual core AMD Opteron64), delivering over 18,000 users and avg dialog response time of 1.87 seconds.  This benchmark surpasses IBM’s benchmark (IBM eServer p5 using AIX 5.3, DB2, 32-way SMP Power5) from May.