I'm looking to go the opposite way. I've had the factory grey turbine 21's since i got the car and I've been considering going to 19's for the smoother ride with the increased sidewall rubber. But rims are ****ing expensive and that's the only reason I've not done it. If mine were in better condition I'd offer to trade with you but I've got a bit of curb rash and scrapes on them from when i let my sister or mom drive.
For tire wear i can say for a fact the 21's wear like *sugar* but I'm 99% sure that is more from the shitty factory alignment than the tire size but i cant be sure. That's why I've done the N2itive and Truhart upgrades. Once i did that all 4 tires wear even and last insanely longer than they used to.