I would say that in general the smaller 19" low profile sidewall tires make the ride a bit harsher than what you get with 17's or even 18's. Surprisingly, the ride was a bit more friendly after I installed a B12 Bilstein/Eibach kit and lowered it as opposed to when I had the AMG suspension on it.
But even now, a 3 or 4 hour drive is tough on the butt and I definitely feel the bumps in the road. But the car sure goes where I point it!
I am running the three piece 19" Asanti AF120's. When I got the car, the chrome was pitting and actually peeling off from the salt air here in South Florida. So instead of replacing, I re-chromed & rebuilt them.
My wheel setup now is 19 x 8 fronts (1.5" outer, 6.5" inner) with 235x35 tires and 19 x 9.5 rears (2.5" outer, 7" inner) with 275x30 tires. I tried going with a 19 x 10 but clearance was an issue.
The fronts started as 8.5's (1.5 outer, 7"inner). But when I lowered it, I changed the inner barrel to the 6.5's so I could move the tire in under the fender a bit more. I found a local guy with a lathe big enough to turn the hub face of the big 19" wheel center. Then I hand fit the assembly for just the right clearance between the shock, the brake caliper, and the fender well.
My rears fit perfect with hardly any room to spare with the 275 x 30's. They are only about 1" taller than stock AMG tire height so the speedo is just about 2mph low at 75mph. Clearance wise a 285 tire would not fit under the fender lip without rubbing the inside rear of the fender well. I know because I also hand fit the rear tires and rim offset.
Lucky for me there is a tire shop right next to the indy who did the drop...
If you cant go to the extreme that I did with rim fitment, I would suggest you stay with a 265x30r19 on the rear. That way if you get an off the shelf offset on your rims, the tires will still sit ok fine without rubbing or scraping.
On the TPMS, my '06 didn't come with it. But you can get valve stems for aftermarket rims that are designed to hold the sensor. When I found out I had to change my instrument cluster as well as get the other electronics I nixed the upgrade and went lo-tech with a $10 digital air gauge.
I'm guessing you're thinking its harder to turn a larger tire and that makes a for a loss of power?
Another effect of a larger tire is the motor will turning at a slower rpm to move the car at the same speed. Lower rpm generally means lower fuel consumption.
All that said, the differences in OE 245/35 tire diameter and the 285/35 being discussed here are 24.8" vs 25.9" That's about a 4% difference.
Since the difference in tire size would not compare to an exact linear reduction in HP or fuel economy you are probably splitting hairs (your probably not going to loose 4% power or get 4% better fuel economy by having a 4% larger tire).
I used this site when I was playing around with tire sizes. Have fun!