I am running 18x8 OZ Crono HT with 245/40/18 Michelin PS A/S3 on my 2013 3.6R...stock is 17x7.5 with Bridgestone Turanza 225/50/17
Current set up (18") is 2 pounds lighter than stock and the rolling circumference is same as stock ...actually marginally different which corrected the speedo inaccuracy the car had when stock.
Ride is a touch firmer, but that is partly due to a larger rear sway bar too.
What DrD123 says is spot on...it all depends on what you put on the car.
Looks like you are driving a 4th Gen wagon?? I had the same wheels on my 2006 Legacy GT where stock was 17x7 and 225/45/17....I ran the 18's on it with 225/40/18....same results as on my 3.6R
Good wheels and tires are the answer if you are switching.
The only REALLY noticeable change is much better road holding/handling