BTFB, why is it too big? You say other shops have said so and you think you are more stretched than other riders. The crucial thing here is notwhat the bike shop or you 'think', it's how you feel. Do you have any aches and pains like; niggling knees, criked neck, lower back pain, sore arms, shoulders, wrists hands to name but a few? If the answer is no then you've nothing to worry about.
I always rode a fairly stretched position - based in part on my old man's 60's racing position (he set up my first bike). When I got a new bike (Spesh compact) the position seemed very upright and very, very odd. But it works perfectly for me. When the old boy has tried to position himself more like me it has created a world ofniggles and aches. Moral of the tale: everyone's different. You've done someserious riding on the bike and I think you'd know by now if it was the wrong size.