At stock settings, under both idle and load conditions, AMA's water cooling kit is able to hang out not only with the top end air coolers, but also the custom water cooling loop built out of high end components. Temperatures aren't exactly impressive, but water, just like air, has it's cooling power limited by ambient temperature. So under relatively light loads, there isn't much gain to be had. I thought the tide would turn in favor of AMA when overclocked, but the performance against air coolers isn't all that impressive. At idle, all four unsurprisingly keep the processor around the same temperature. However, this all changes under load. AMA's kit just can't keep up with the custom loop or even Thermalright's cooler. Fortunately, it doesn't claim the last place and is able to shave 3 degrees Celsius off Noctua's flagship heatsink.
http://www.overclockersclub.com/reviews/ama_aragon/