4gb single channel vs 3gb dual channel

Solution 1:

From my point of view, 4GB single channel will be better.

There is a very small number of applications ever capable of reaching the speed limit of a single channel, while more memory will be better for all applications.

Solution 2:

More often than not, the 4gb option will win out.

Even if your primary apps aren't using the 4th gb directly, the OS will use the left over ram as file cache, speeding everything else up more than you'd notice the dual channel difference.

This wouldn't apply for very specific science things designed to use that memory channel efficiently.