Can you please give the exact model numbers or links to the 2 CPUs.
Generally it would be a massive improvement. In most cases when moving to a deul core performance will double if apps support 2 threads/cores.
You will also benefit in many other ways, you will be able to tab (alt+tab) between applications with minimal lag and less RAM usage.
But the actual performance differance is relative and to give you an idea we need the exact details of the CPUs.