285/30/19 is perfect for the rear when paired with 245/35/19 up front. The 275/30 has too small of a sidewall- However the 275/35 is tooo much sidewall-just like the above picture-why would you wnat to rub when you turn? The ride is perfect with teh 285/30/19, you can adjust your tire pressure for a more comfortable ride-plus it looks wayyy better-look at the pic above-wayy too much tire and not enough wheel-you dont want your car to look that bad

 

hey xenon the car looks really good with the m6 reps...almost making me re-think suggesting you to go with the 20" swiss.

If you dont HAVE to run a 30/19 then dont. Adjusting tire pressure to make the ride more comfortable on thinner tires risks bending your wheel. The tire wont absorb the shock from bumps if you reduce the pressure to make it softer. It will also decrease your mpg and accel. This is something I used to do when id go for a spirited drive through the canyons in my mini.

275/35/19 is perfectly fine, and most people run that. Unless you have a specific look you're going for, which it sounds like you dont, then that size is good for your setup.

I run 275/35/19 in the rear on h&r sport springs, and i dont have any rubbing.