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.

He's right but get this..
 

bobiam is correct but in my case The Tire Racks recommendation for snow tires for the SLK230 was absolutely dangerous. Add to that the fact the tires were the same brand and Tire Rack said " these new Blizzaks should be compatible with the Blizzaks you have on the front.

As one of the other posters offered, the front and rear of the car acted like they weren't connected to one another and the car wanted to change ends, if you made any sudden turns with the steering wheel.

Totally wrong information from them and I won't do business with them again. Their recommendation was dangerous to say the least.

So if you want to mismatch brands go right ahead it's your life, just let me know what roads you take so I can go a different way! :D

Anyone ever drive a car with a spacesaver spare tire? Did you adjust your driving accordingly? How about a new Cayman R with a slow leak in the right-rear tire, leaks to 10psi? Drive your 1967 El Camino SS 100 miles on the freeway at 85mph to buy a used refridgerator & drive 85mph back home? Are any of these vehicles unsafe to drive? Does the driver need to make adjustments to their driving style to allow for the reduced capability of their vehicle? A driver should never exceed the capability of their vehicle or driving skill. It's like building a race engine: the weakest link will break first. Tires are no different, if you choose to downgrade the handling capability of your car you must adjust your driving to suit the weakest link.

I haven't had to replace the rubber on mine yet. Why would the rear tires wear at a rate 2:1 faster than the front? According to one poster and not previously challenged or questioned. Very curious.

The rears typically wear faster than the fronts since they are doing all of the work in moving the car (propulsion) and Porsche drivers tend to be a little (hah!) lead-footed. And the majority of typical driving is mostly in a straight line so the fronts are just along for the ride and not really doing much work.

Fronts will typically wear at the same rate as the rears if you are doing a lot of canyon carving or other driving where you're spending a lot of time cranking it in the corners. In this case, the understeer built into the car will cause the fronts to scrub and wear at a rate similar to the rears.

If you track at lot, you are cornering hard on a fairly continual basis so you may find the the fronts wear even faster than the rears, especially if you haven't adjusted your tire pressures correctly and/or increased negative camber to minimize understeer and even out the wear across the tire (inside to outside).

Thanks for that. I spend half my time in the city and half in the mountains - so I guess I'll see what comes of my situation. Unfortunately the "wider in the rear" set up eliminates the ability to rotate all the way around.