Front Primacy 3 and rear MC6.. what is the danger?

ya hoh.

the performance cars, staggered rim somemore + diff width.

If straight road usually not much impact, but if your in high speed doing cornering and some emergency happen in the middle that will be the best time you pray your tires and brake system perform well.. 

Usually normal driving condition, mix different tires wont have much impact. But still at least front 2 or rear 2 need to be same.
If all 4 tires different brand or treads, if not mistaken can be saman by JPJ and go for puspakom inspection. (usually will fail brake test as 4 different tires will got different braking distance if different compound)

The uneven brake pad wear level already a big indication, just as per mentioned before if went for brake test different tires will come out different results. Why i know, as 1 time i forget to change out my spare tire and during puspakom inspection gg brake test. If you see the test report from puspakom they can show you individual tire braking performance which 1 is below par thus why is better to have at least both side or better all 4 the same tires for even braking performance. What i believe if the 1 tire braking performance is worse the brake pad on that tire side will wear even more.