I grip the actual plates, and not the bar at all. It gives me a more full work out, due to my having to keep the bar from falling in all directions. It also allows me to seriously work my grip strength, especially when I use bumper plates. It's not for everyone.
If I'm correct, on the Rogue bars, the inner rings are the power rings. The outer rings are the Olympic snatch rings. So if your index finger is on the inner rings, you're legal. If you're anywhere narrower than that, youre also legal. If you can see the inner ring inside your grip, you're illegally wide. To be sure this is correct, measure the distance between the inner rings. They should be real close to 32 inches apart. To be exact, they should be 81cm.
For giggles I put my index finger on the inner ring during one of my bench warmups today. It was uber uncomfortable...
Yes, index fingers on the inner (powerlifting) rings is the maximum (although not necessarily advised) allowable bench press grip. The markings are at different spacing because there are two different sports with different rules (which they must have, since the contested lifts are different). So they have their own markings to fit thoae rules. Thus a dual-purpose bar, like the B&R, needs to have both sets of markings, and they just let them look the same under the assumption you can figure out which ones are "inner" and ones are "outer" based on the sheer intuitive powers of our giant mammal brains.