Now, i have a different theory on this all together because of my backgorund. I race dirt late models, the tranny is set at zero degrees, the pinion is 7-8 degrees down at ride height, and they are NOT aligned at all height wise, probably a 2-3 inch drop. Now under power with the bird cages on a full floating rear end, they by theory align the pinion and trans to the correct angle and all that, but, anyone ever seen how much these rear ends move? If the rear end was already lower by 2-3 inches and it drops even MORE its never lined up. All this perfect angle stuff sounds like BS. Those rear ends move 4-5 inches side to side, and a foot or more up and down, and 4-5 inches FORWARD, theres no way the pinion and trans angles are EVER the same or in line, and we NEVER have any problems. Get it close, set them the same angles (Pinion up and Trans down) at ride height, get it centered, and don't worry about it. I am assuming with Coil overs that you are running a 4-link? Darn near impossible for pinion angle to change. If you plant the tires hard, the whole car should raise, thus ruining your alignment both height ways and side to side (assuming 4-link and panhard bar) anyways, but it would rotate the pinion up if anything, so if you are at 6 degrees down on the trans, go with 4 degrees up on the Pinion. Planting 800+ HP we aren't having problems, use quality parts (especially good U-Joints) and you won't have any problems. Obviously different vehicles, and yours will have no where near the movement and changes, but if that can survive and function, your set up will too. Look at a IRS set up, those are short drive shafts essentially, they see way more change than your drive shaft will and they function with out problems.