First off. You need to read this entire thread:
Guide to fitting wheels and tires to the 2011+ WRX
Secondly. You aren't fitting any 527's without fender modifications. 18x8.75" +35 is going to stick out about 1.1" further than your stock setup. With that much sticking out you will rub even on stock suspension and if you lower you WILL DEFINITELY need a roll and pull on all 4 corners. This gets even worse when you bump up to the 18x9.75" +20 which will stick out about 1.7" farther than the current setup and will require coilovers to fit because camber will be needed. Also running a +20 has some ramifications with regards to steering and steering feel. Go read articles about numb turn in and scrub radius. You need to do lots of reading before you go willy nilly buying wheels. Also, XXRs don't have the greatest reputation. You have to question the manufacturing and metallurgy of wheels that are ~$160 each.