I should have mentioned that www.tiresize.com was the tool I used to make my decision. It has a tire dimension comparison calculator that should the differences between what you have and what you are considering.
for the rims, I shipped online and printed the best price and America’s Tire store matched it.

 

Those 15" wheels look awesome! Much more proportional to car's shape than bigger 18" wheels with thin tyres.

Did you get chance to weigh those 18" wheels & tyres to compare to 15" set? Extra weight from larger wheels & tyres cause worse ride-quality. Extra weight comes from replacing rubber & air of original wheels with metal. This extra mass pushes up on body of car with more force when hitting bumps & holes, causing ride harshness.

Also shorter sidewall from 50-series tyre is less flexible and doesn't absorb impacts as well as factory tyre's taller software sidewall.

 

No I didn’t. They were sold as quick as they came off the car

 

Those 18" wheels & tyres probably weigh 6-10lbs more per corner than lighter 15" combo. Really destroys ride-quality and handling.

I really like Enkei RPF1 wheels. Typically lightest you can find in any given size. I'm looking at getting set in 16x8" ET38. Weighs 6.5 lbs less per corner than factory 15x6 steelies.

 

Yeah mine came (used) with Enkei 18's, and I'm looking to sell them so I can get some aluminum 15's so they're lighter.
Bigger ones look cooler, period. As in, looks are the only thing they are better at than 15's.

 

You're forgetting the other big advantage of 18's. They ride like a floor jack.

 

Personally, I prefer phat wide tyres look myself...