Would it be better(result in a cooler OC) to bet one of those GPU with a powerful cooler on it and take up and extra slot due to it or just get one w/ a regular old fan and buy a case fan to cool it?
Any card with a good aftermarket cooler on it will run cooler than a stock one.
GPUs aren't really limited by temperature for overclocking though, so you can't just drop your temps 30C and then overclock them and raise it 30C again for a way faster card, they just don't overclock very far.
4670 is a pretty slow card anyways, even if overclocked cant get very far, dont waste your money on cooling, the iceq is good enough, if i were you wait till dx11 cards come out