With dual fans and a reasonably large copper radiator, and the radiator being mounted externally.... it should be ok.
Also not mentioned, but it plays a role is your pump(s). Have you got enough flow? Also with a single cooling solution for both your CPU and GPU you're going to have be careful with the routing of the water. Don't want to super-heat the water and then try to cool another component.
But given that you already have the radiator, there is no sense in planning to replace it until you test it. At stock, even a basic cooler will work. So approach overclocking cautiously, don't use too much thermal paste (the classic rookie mistake), and you'll know soon enough.
I've given up on water cooling for now as a poor investment of time and money, but I've done custom loops for the entire system. I've done separate lower end coolers for the CPU and GPU. Two lower end ones beats one good one most of the time.