Question : Problem: Intel Xeon EM64T or AMD Opteron ???

At a first look i read that Opteron performance is up to 30 % faster than Intel Xeon EM64T, and prices for AMD Opteron in the same hardware vendor ( HP ) are cheaper. Is AMD Opteron really performing faster and is the correct election ?

Answer : Problem: Intel Xeon EM64T or AMD Opteron ???

Yes, AMD is really taking advantage of Intel's limitation in pushing the speed envelope:
http://www6.tomshardware.com/cpu/20040927/index.html

Even the Athlon64's that are not FX or Opteron cpus are performing very well against their Intel counterparts, and they are running cooler while Intel Prescotts are running hotter.

Athlon 64 compared to other cpus
A64 2800+, 3000+, 3200+, 3400+, AXP 3000+, A64 FX51, A64 FX53,
P4EE 3.2, P4EE 3.4, P4 3.2, 3.0, 2.8, P4 3.2E, 3.0E, 2.8E
http://www.anandtech.com/cpu/showdoc.html?i=2038&p=1