Jason Stacy wrote:

I wonder why a two-core CPU with lets say 2 * 1.7 Mhz
is theoretically faster than a single core with 3.4 MHz.

Because it is in practical situations.

I am NOT talking about additional features like Pipeling and
Hyperthreading but the core fact that the power is split over two cores.

Assume the following situation: A NON-THREADED application
needs as much CPU power as possible for some computations.

Thats not the situation where a dual core processor is theoretically faster.

On a 3.4 Mhz machine it can occupied almost 99% of
the CPU power (remaining 1 % are for system services).

When I run the same application on a two core system then
it can occupy only ONE of the two cores with 1.7 MHz. Because
it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?

No, just looking at the wrong situation.