John, working angles are that important. 7 degree working angles will net you a very good vibrator for a car. They would work pretty well on a post hole digger.
You also need to consider your headers when raising the driveline to far along with other things like hood clearance. You really need to find the sweet spot and it may not be by the book.
In these circumstances which everybody runs into on a muscle car that has been lowered this far from factory, you need to concentrate on getting your working angles as small as possible. Preferrably under 3 degrees at ride height. Find the sweet spot for your driveline and start playing with your pinion angle and keep an eye on your driveshaft. You must get it flat(Close) or sloping down towards the rear of the car so it decreases your angles, not increases them.
I'd try 2.5-3 degrees of driveline angle with 0 pinion angle to start. Once you find your sweet spot, remove your springs from your shocks and run it through compression to make sure you have the clearance needed around your pumpkin and driveshaft tunnel.
Keep in mind that your U joints need a minimum of .5 degrees of working angle to prevent premature failure. I'd also like to see your front and rear working angles as close to .5 difference as possible. (Front working angle is 2.5 while back is 2 for example)
When you lower your pinion angle, your wheel will move towards the front of your wheel well. You may as well make the fore and aft adjustment once you find that sweet spot as well.