Physical cores are number of physical cores, actual hardware components.
Logical cores are the number of physical cores times the number of threads that can run on each core through the use of hyperthreading.
for example, your 6-core processor runs two threads per core, thus you have 12 logical processors.
In your initial question you were asking about the actual speed. The clock speed of your computer is 3.5GHz x the no. of cores, so your speed would be 3.5GHz x 6 physical cores. The higher the clock speed, the more operations the CPU can execute per second.
This page can explain how to calculate processor speed on multi-core processors.
I found this forum that might have the answer you're looking for.
The best answer starts like this:
Physical cores are just that, physical cores within the CPU. Logical cores are the abilities of a single core to do 2 or more things simultaneously. This grew out of the early Pentium 4 CPUs ability to do what was termed Hyper Threading (HTT)...