Can I notice the performance difference between 2x4GB 1600 sticks and 4x4GB 1600 sticks?

Solution
no, I would be more worried about my hdd speed.

Ram speed is thousands of megabytes a second, most hdds are not even a hundred!

your device is only as fast as its slowest component.

buy whatever is cheaper, and spend the rest saving for an SSD.
no, I would be more worried about my hdd speed.

Ram speed is thousands of megabytes a second, most hdds are not even a hundred!

your device is only as fast as its slowest component.

buy whatever is cheaper, and spend the rest saving for an SSD.
 
Solution
No, you will not notice a raw speed/performance increase, but if your doing video work or using Photoshop more memory is always better because those can fill up your memory very fast depending on the size of your workload.

What will this PC be designated for?