For auto-x i see several issues tho. Aside from getting kicked out of stock classing.
1st problem: 17's and 215/40/17's vs 19's and lets say 225/35-ish something. I would lay money that unless you're going to spend super, super $$$ on that 19" setup, you've gained a ton of (unsprung) weight. So, traveling in the wrong direction. Might look good, but bad for performance. So there's -1
2nd: Like he said, trying to reduce overall diameter to add low end grunt is not benefited by 19's. -1 again.
Lastly you'll go faster by adding more rubber (bigger contact patch) or sticker rubber. You'll increase your traction for acceleration, cornering, and braking. And since cramming huge wheels under cars usually requires using stretched tiny tires, that's not gonna help either. -1 yet again.
Again, not to say that you can't auto-x on some good looking, bigger wheels n tires. I'm all about enjoying auto-x without being overly competitive (takes all the fun out of it). But that does not make for a faster car.
Hmm. my thoughts on auto-x'ing BRZ if i had one: swap to 4pot/2pot setup, get 15x8 Slips's with 225/45/15 RS-3's.
Fender gap much?