I think you would be far better buying a Wicked Ridge, Parker, Excalibur or TenPoint crossbow Barnett crossbows are pretty much junk/ They are cheaply made and tend to break, blow aprat and otherwise fall apeart, They are not built to handle the speed. The trajectory is not even close to what the Bozo from Cablea's told you.
Do yourself a favor and contact Wyvern Creation, 603-659-0575 it will be the best phone call you ever made. David will give you the straight factual info and help you make the right decision buying a crossbow