What offset are they?
A wider rim does not, on it's own, increase the contact patch much. It mostly just lets you run wider tires. 17x7.5" is fine if you're planning on 225/45/17 but you'll need 17x8" with a nice offset (at least 48) to run 235/40/17 or 245/40/17.
Rim width is really only a tool to run wider tires. If you have the tires you want, get the lightest rim you can. That and make sure the offset is as close to stock as you can find (generally) which is +53.
2015 STi: Still Stock
04 STi, 04 WRX: SOLD