Ah, sorry. Should have read the whole thing. Depends on the airplane of course, but you´re basically flying a big single when you over load most light twins like that. the Ferry permits are kind of based on the premise that it´s going to be a one off and the chances of having something go wrong for the relatively short time you´re overweight is slim. I´ve flown twins overweight, though, and you´ll find the performance will deteriorate very rapidly indeed when you get over gross.