I am pretty sure that the outer diameter of the tire is the same, so there should be no difference in RPM. The bigger the rim the thinner is the rubber sidewall. A lot of people say this results in choppier, noisier ride. The 17 inch rims will also save you money when the time comes to buy new rubber. Anything that fits on 19s is considered low profile and "exotic" so normally the prices are higher for those tires even though performance can be identical. It's kind of funny how the fashions have evolved. In the 90s, a midsize car came with 15 inch rims standard, and 16 were premium. I kind of hated the 15 inch rims because they won't clear any decently sized disc brakes. In early 2000s, the 16s became standard, and 17s were premium. Now it looks like 16-17s are standard, and 18-19s are premium.
All the car mag review I read said that the 19's make for a harsher and noisier ride than the 17's. Mazda should offer the 17" option on the Touring model but from what I read the 17's are available only on the Sport model. That was one of their gripes during the testing and review of the car. The 19s were harsh and hitting bumps jarred the car and made for more road noise when above 60MPH. The one editor stated that Mazda should have gone with a 18" rim, sort of a compromise.
I would also state that the 19" low profile tires will wear A LOT faster than the 17" taller profile tires. Depends on the tire but a 19" might need to be replaced at 30k vs 50k on the 17".
Maybe Mazda will offer the 17" for 2015 on the Touring and GT models? I had 19" rims on my Corvette and the tires were EXPENSIVE and the ride was tough. I currently have 17" on my Mazda3 and they are just right.