IDK about the G because I've never run anything less than 93 in it, but the 03 Murano a friend of mine had would labor-knock on 87 or 89, and you would think being a crossover the VQ35 in it would be tuned more for 87 than a G35.
He was also telling me about a dyno test where the Murano gained 3hp from 93 vs 87. Or maybe lost 3hp from 87 vs 93? Whatever, the point is the motor wasn't making as much power as it could because it was pulling back timing because of the knock sensor.
My 94 Trans Am would run on 87, as do my Mom's 95 and 96 Suburbans. But My 00 Trans Am with the LS1 HATED anything less than 93, it would knock in 5th and 6th up every hill. There were even a couple of stations where I fueled up with what said 93 on the pump and it would labor knock. Needless to say, I don't buy from those stations anymore! (kinda makes me wonder if it was an additive causing that or they were lying about the grade)

 

The octane stickers on pumps are put there by marketing department.
All a premium means is higher than a midgrade which is higher than a regular.
The posted numbers are usually within +- 1.5 blended average octane points, But that often depends on how long the fuel has been from the refinery to flowing into engine.

For example gasoline may be 2 weeks old from Houston to our ATL tanks.

Many times the posted octane is a function of sealevel vs altitude [ATL at 1000' vs coastal] can show 2 points difference [93 vs 91].

 

Gas does suck when it sits. Kinda makes me wonder with them putting more ethanol in the gas now, ethanol soaks up water. If you put 99.9% in open air it will very quickly start drawing moisture out of the air. I wonder if this is the case when it's mixed with gasoline. I'm not going to claim it does by a long shot, but it does make me wonder.