We did real production benchmarks using different servers. Servers were put into production behind load-balancers, then weights on load-balancers were changed so we got highest number of dynamic PHP requests per second. It must sustain that number of requests for some time and no drops or request queue were allowed. With static requests numbers for Opteron and T2000 were even better but we are mostly interested in dynamic pages.
T2000 is over 4x faster than IBM dual Xeon 2.8GHz!
Except x335 server which was running Linux all the other servers were running Solaris 10. Our web server is developed on Linux platform so it's best tuned on it. After fixing some minor problems web server was recompiled on Solaris 10 update1 (both SPARC and x86). No special tuning was done to application and basic tuning on Solaris 10 (increased backlog, application in FX class). Web server was running in Solaris Zones. On x4100 and T2000 servers two instances of web server were run due to application scalability problems. On smaller servers it wasn't needed as CPU was fully utilized anyway. Minimal I/O's were issued to disks (only logs). Putting application into FX class helped a little bit.
Perhaps putting application in a global zone, doing some tuning to Solaris and application itself plus tweaking compiler options could get as even better results.
For more details on T2000 visit CoolThreads servers web page.
You can also see SPECweb2005 results which do include T2000.
1. IBM x335, 2x Xeon 2,8GHz (single core, 2 cores total)
2. Sun x2100, 1x Opteron 175 2,2GHz (dual core, 2 cores total)
3. Sun x4100, 2x Opteron 280 2,4GHz (dual core, 4 cores total)
4. Sun T2000, 1x UltraSparc T1 1GHz (8 cores, 8 cores total)
5. Sun T200o 6x, 1x UltraSparc T1 1GHz (8 cores, - two cores (8 logical) were switched off using psradm(1M).