Actually, Iran's rise is really bad news for China. China's economy can't grow without oil. And most of China's oil is imported. Its top oil source is Saudi Arabia. Its second is Iran. The only way the oil can get to China by sea is through the Persian Gulf into the narrow Strait of Hormuz. Iran sits on the Strait's northern shore. Any armed conflict with Iran would effectively shut down the shipping lanes and put a serious crimp on China's oil supply. Very bad for Chinese national security.
China is taking a very risky gamble on Iran. It has bet the economic farm on a stable Middle East, yet its second largest oil supplier is the region's most de-stabilizing force. China doesn't hold all the cards in this game. In fact, they're all in, and very exposed.
China desperately needs the rise of a peaceful Iran -- not an adventurist, militaristic Iran. Here, the US and China's national interests strongly align. We must work together with the Chinese at the coming G-5 plus 1 talks to corral Iran's weak regime into becoming the kind of regional actor that is safe for China's energy security, and therefore safe for the world.
Remember, sanctions that bite Iran will bite China, too. To work at odds with China, which still holds a lot more leverage over Iran than we do, would be a near guarantee of failure.