I absolutely love my flex, 400hp can be done without turbo upgrades. I have no idea what the weight difference is between the sho and the flex. I read somewhere that the engine is good to 700hp, but don't know how accurate that is... as for power through the trans??? I would say you have to worry about the PTU over anything else. I couldn't tell you what my flex has for power since I have no all wheel dynos in my area unfortunately. I may have to take a drive someday. I too would like to do the upgraded turbos with what I already have but that damn PTU worries me. But I may just bite the bullet. Good luck on your decision. but I can assure you that you will love the flex.. You will have more people than me respond that know a hell of a lot more than I do.