PRAGUE (Reuters) -Executives from Boeing ( BA ) and Airbus dampened speculation of imminent decisions to replace their best-selling narrowbody models, telling a major audience of investors that it would take time to achieve the required jump in performance.

The Wall Street Journal reported last week that Boeing ( BA ) was in the early stages of developing a 737 successor. But marketing chief Darren Hulst told the International Society of Transport Aircraft Trading that a launch is "some way off" while a senior Airbus executive said it would "take a bit of time" to achieve the 25-30% efficiency gain needed to attract the market.

Both executives were speaking in response to questions on stage during an ISTAT gathering in Prague.

(Reporting by Tim Hepher; Editing by Emelia Sithole-Matarise)