I was wrong about the fender rule. It doesn't say anywhere that you have to fit the tire under the fender. That should open up some options for 18x11. I mounted 315 on my current wheels today pretty easily. No rubbing and due to the shorter height, a little bit better clearance. I'll take some pics this weekend if I can get the prep on the car done in time
Here's some of the tires mounted
315 on 18x10.5
https://photos.app.goo.gl/QU9b3DN8rLGgWyox7