I've found a lot of the memory to be of a different quality too. Generally the Rx cards perform much better for me. Keep in mind, at the factory a lot of the cards have IDENTICAL hardware, and then they test them at various clock speeds. Some work better than others, and that's often the deciding factor if a card gets branded as an OC model or not. Ultimately that's the result of imperfect manufacturing techniques. Same thing applies to processors and basically everything that uses today's ultra small fab processes.