This seems to be the best summary I've read.
Quoting a guy called "NoDamage" at SPCR forums :
The general trend seems to be that the Accelero X2 is a better cooler than the VF900 for this card. The Zalman at 12V does perform better than the stock cooler and the Accelero when they are set to auto fan control. However, when they are set to 100%, both the stock cooler and Accelero outperform the VF900. The Accelero at 100% also tends to equal or outperform the stock cooler at 100%, so it seems like the best choice for this card. The reports of the VF900 causing crashes or overheating when paired with a X1900XTX are also fairly discouraging.
In terms of noise, I think the Accelero has a huge advantage over the VF900, V-1 Ultra, and Sytrin VF1, because it is the only cooler that is powered by the video card. It is supposed to be fairly quiet at 100%, but you can have ATI Tool dynamically adjust the fan speeds between 2D and 3D mode and throttle down the fan to be completely silent when you are not using it.
The auto fan control issue also helps explain the conflicting results in the earlier reviews. The performance of these coolers is highly dependent on the fan speed, and the default fan header voltage may vary from card to card. For instance, on the X1900XTX it is usually under 50% most of the time, only cranking up to 100% when the temperature surpasses something like 100C, which virtually never happens. With a cooler like the Accelero connected to it, it may not perform too well since the fan is turned way down by default. The VF900 on the other hand goes directly to the MB/PSU, so its fan speed is generally consistent across all reviews. So on a card with default low fan voltages the VF900 will tend to perform better, while on a card with higher voltages the Accelero will fare better.
