Speedo is more normal because you are now only .6" off in the back where it reads vs 1.3" off. ABS light may or may not come on but don't be surprised if it does because your front tires are spinning much faster than the rears. If you like it, cool at least you didn't get one of the AM canned combos that have the fronts bigger than the rears.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.