This is always an interesting topic, reading opinions as different as the colors of a rainbow.
FWIW I'll throw in my 2cents as I am sort of the crash test dummy of tire choices and mix-n-match. So far just tests, no crashes
I have rarely run 4 of the same tire on the street.
First of all the OP is on 19s so he has few good choices and they are all pretty $$$$. Of the size he needs only the Bridgestone Potensa RE050A will be a close match in terms of wet traction, ride quality, and dry grip. The Continentals will be ok but not much savings so might as well stick with PS2s. The Nitto Invo is a decent tire but not a close match to PS2s. I would not put 2 on the rear. None of the other tires mentioned as substitutes in this thread are available in that size. This was a pretty good comparison test for those of us on 17-18 wheels:
http://www.caranddriver.com/reviews/comparisons/09q2/tire_test_nine_affordable_summer_tires_take_on_the _michelin_ps2-comparison_tests
Over the years I have swapped mismatched tires around a lot and while most have been a pretty close match, a few sets were horrible. For kicks we ran a set of Conti Sport contact 2s on the front and put on a set of Kumho All Season tires on the rear and ran a session at Spring Mountain to see what would happen. It was terrible... like driving on unpredictable ice with a lot of breakaway oversteer. I managed a few off in the dirt moments and decided these tires didn't play well together. We pulled the Kumho's and ran Sumi's on the rear... balance restored. A good match and the tires were excellent on the dry track and even later in the rain.
I am currently running out an older set of Pilot Sports on the front and put Nitto NT05 on the rear on my 17 street wheels. The Nitto's have a much higher level of dry grip and are pretty good in the rain. They are more of an extreme performance tire than the Pilot Sport so the result is more "push" and the ABS will kick in early under heavy braking in the wet or on painted surfaces. I can live with that on the street. The NT-05 rears never let go. Once I finish off these front Pilot Sports I may go with NT-05s all around.
I guess the moral of the story is: if you are going to mix-n-match, make sure your rears have better wet/dry grip than your fronts and the car will be predictable. The closer you match tread style and tire compound, the better your balance will be.