Even with 50% fan speed, it runs much cooler than stock. You'd be surprised how low the stock fan speed tends to be.
Of course that also means that no matter how high you crank it over stock, it won't really get any hotter, the fan will just spin faster (if you don't manually bump it up). That's how my 4870x2 is - no matter what kind of load you put on it, as long as it's above idle, it runs 90C. If I'm running Command and Conquer Generals, it runs 90C, but at 35% fan speed. If I'm running Crysis, it runs 90C, but at 50% fan speed (oh, and it's a freaking vacuum cleaner at 100% fan speed, which it luckily never reaches on auto fan control).