looking at getting an encoding rig
 

what setup will allow faster encoding
one with a 2.8ghz dualcore or one with a 3ghz hyperthreaded processor

One encode session with a 2.8ghz dualcore processor will be slower than one session with a 3ghz hyperthreaded processor.
Two encoding sessions will be faster with the 2.8ghz dualcore processor than two encoding sessions with a 3ghz hyperthreaded processor.
You choose :)

-kwag

so in otherwords i can encode 2 videos at the same time at the same speed as the 3ghz hyper threaded????

A dual core is a physical pair of processors (they really exist in the chipset). An hypertheaded is a virtual pair of processors (they do not really exists, but the single processor can be used in a way that you will have the idea that you have two processors).

What Karl means is that the real pair will be faster that the "false" virtual one even with the lack of 0.2Mhz.