Difficult, in theory because you should find it easier to run on pavement as trails are more effort but will your feet stand the pounding? I've done a half in brand new shoes and got away with it, you have a choice Do one long run on pavement to see how it goes, but what happens if you injure yourself? Start building up the mileage on pavement to see how it goes Theres quite a while until the race I would go for option one but I'm not right in the head. By the way looking at your avatar have you got a foot fetish as well? My photo is the end of the London Duathlon last year my wife said I was going too fast to pan the camera,