[ntmatter]

I'll move this note to the front of this post because I realized I got into a bit of a rant and want to stay on-topic: Wider is not necessarily better for handling. The 5mm spacers would be great to make the car look cool, stay away from anything bigger until you've at least tried these.

Anyone who says that wider is always better is uninformed. Wider MAY be SOMETIMES better for CERTAIN applications, but you want to be careful. Picture in your head the interaction of the upper and lower control arms, shocks, steering linkage, etc as your wheel travels through it's full up-down range of motion. Imagine the industrius Germans wearing white lab coats in huge computer labs refining the exact angles and positioning necessary of the entire suspension system to get the best weight distribution and chassis handling through all of the suspension loading scenarios. These calculations take into account the mass distribution in the car, the flex and other characteristics of each part, the behavior of things like wheel bearing under load; in short, a lot of planning goes into the stock setup.

Now, move the tires out an inch or so but don't change the spring rates, shock load and unload rates, steering geometry, or alignment settings. If we're talking a 5mm space you'll get a nice look and probably won't notice much if any difference one way or the other under most street and even track scenarios. But, if you move the wheels out 30mm each, then the car's just not going to handle right if you really get on it.

I've tried to use spacers on my last track car (not a Porsche, but same principles) and in the end couldn't get around the fact that spacers ended up making the car look cool but caused problems. These included some nasty torque steer, rubbing the wheel wells, weird handling, and I kept burning up wheel bearings and breaking lug bolts.

As with fancy air intakes, you can do them for the performance look, but be realistic in your expectations.