When going 30 it will say you're going 28.893mph. A 40 profile on the rear will put the speedo out by -3.69% so not a huge amount at all.
T/C will kick in a lot more.
No it won't. A staggered set up means that as the fronts are narrower, they instinctively want to stay there, in the front. It's designed so that any billy can drive the car safely. Bearing in mind that if you don't have rays alloys you have a square set up anyway, I don't think it's going to affect the tcs, abs or any other safety system at all.
Can't a guy exaggerate these days