That's quite a jump in wheel size from your OE setup. Your tire aspect ratio is going to be very "rubber band tires" in order to maintain the same OD within less than one percent difference.
If I were going to change wheel sizes deliberately, I'd go square. The staggered arrangement is, as far as I understand, all about enhanced handling. It reduces understeer. Do I have that right? Anyway, it is more theoretical and subjective than real, imho; because 99% of drivers will either never push the car hard enough to test/tell the difference between square and staggered, or couldn't tell the difference even if they did push hard enough.
The main reason why Kia offered a staggered setup is because wider in the back makes the car look cool. But you lose half your treadlife warranty if you have a staggered setup. So why deliberately do that? Well, in my case, I didn't want to change the way the car was designed. I'm conservative that way. But I did allow a half inch wider in front and a whole inch wider in the rear, while keeping to 19" rims, when I bought my "summer" rims. So, I guess I'm just talking about options here: and I've already decided for myself.
But if I were going to 20", I'd go square, and wider. Make sense out of that!
