By Adam Jourdan SHANGHAI (Reuters) - Four Chinese investor groups are locked in a more than $140 million bidding war for one of the world's most powerful soccer agencies, UK-based Stellar Group, a source said, a sign that China's appetite for sport is outgrowing trophy club investments. According to documents reviewed by Reuters and a source with direct knowledge of the talks, the Chinese bidders include model car maker Rastar Group , which last year bought a majority stake in Spanish soccer club Espanyol. The potential investment would be music to the ears of avid soccer fan President Xi Jinping, who has an ambition to host and one day win the World Cup. More...