If your system really needs a RAM upgrade will depend a lot on the daily used applications. But it pretty possible that you can run out of resources with just 4GB installed. From that point on the system needs to work with the available virtual memory. The latter is far slower as the data is stored on your HDD/SSD in stead of in the RAM.
First test we use Superpi32M as it loves bandwidth. Huge bandwidth means overall a snappier system, however don't expect miracles to happen as the slowest component will determine the overal behaviour.
If we compare the single channel 1333MHz versus the Dual channel setup we directly spot a huge increase in calculating speed. The speed increase from 1333MHz to 1600MHz results in a over 14 secs faster output. However the gain going to our overclocked speed of 1866MHz is far less.
Wprime hardly depends on bandwidth and is in determined by raw processor speed. We see a maximum difference of a second.
The AIDA bandwidth test tells the same tale as the SuperPI 32M chart. A massive increase from single to dual channel operation. A milder gain when upping the ram speed to 1600MHz and again to 1866MHz. when we run the CPU Queen test we see the same behaviour as with WPrime, if it's purely CPU, more or faster RAM hardly changes the output.
But the PhotoWorXX test, which performs different common tasks during digital photo processing, sees a good boost coming from single channel and scaling with some extra RAM speed. Again it depends purely on the programs and operating system you are using if you will notice a speed gain yes or no.
The X264HD version 4.0 Video encoding test also loves more and faster RAM, though once over 1600MHz it hardly benefits anymore. Cinebench R10 is one of them CPU only tests, it all remains within the margin of error.
We tested Mafia II at high detail preset and Crysis 2 at the GAMER preset, both games running at full HD resolution, so the GTX670M had to work hard for it's money. As with all games hardly anything spectacular happens. More and faster RAM can decrease loading times, but in most cases hardly boost your Frames Per Second.
Time to wrap it up...