Well, my point is not to buy a nice fancy cooler when you could save. Pay $50 for a couple extra FPS, I wouldn't.
Absolutely, but if OP already has the card, a better cooler is justified, even if not overclocking. Idle temps on the HD 4800 series were ridiculously high, and way too high when stressed. I burnt out a hard drive with my HD 4890 because my ambient temps were too high for too long (it was even an ASUS DirectCU cooler).
Senpepe, you will not be able to clock the HD 4870 up to 6870 performance, but you could probably coax 6790/7770 performance out of it with a 15% overclock. You'll need a decent cooler though - check out the reviews on this one.