buying 2 indentical sticks instead of one with bigger amount of memory also gives you a small (but visible) boost in efficiency. No matter if its gaming, Cidebench or professional work.
And about that recommended - since 3200 MHz boost in efficiency is no longer good enough to satisfy much higher cost of the ram. Below that it's better to buy faster, than save some money. If you only can afford 3200, go for it. Even 8gb (2x4) will be enough to operate it at the start. Overclocking MIGHT, but don't HAVE TO work. 3200 tested and sold as 3200 HAS TO work, otherwise the product is bad and you will get a replacement.