It is marginably faster. I usually advise using exactly two RAM sticks, for the following reasons:
1. You get dual channel. Almost no improvement at all, but since there is nothing to lose from using it, might as well do it.
2. If one stick fails, you still have a working PC. This one is a major benefit.
3. If you use more than two, there is a greater chance one of them may malfunction during the PC lifecycle, giving you all sorts of headaches.
So use 2 memory sticks with enough capacity.