eh... if you are getting a newer Cadillac DeVille, then just run premium... don't cheapen out on it...
yeah, the knock sensor can retard the timing.. but it is more of a safety thing to prevent further damage to the enigne.... in other words... you can use cheap gas, and have the knock sensor do it's job, but Kat said the end result of what would happen...
... think of it as being an object... any object, this object has a primary system and a secondary back up system... I dunno... lets say a motor mount... if the motor mount breaks, there is still a bolt built into it to prevent the enigne from jumping too much... and practically coming out of the car.... insead of fixing the mount, you just keep driving around with it, everytime to accelerate the engine jumps around... until one day after abuse, that secondary system will fail and that bolt will snap... a corny comparison, yes, but that is what is basically happening when relying on the knock sensor to prevent pre-ignition....
... Last winter when my Olds was my only car, I ran premium all the time, dosn't even require it, but I did... the 3800 has a knock sensor too... now I run regular, as that engine will not get any benifit from premium... I used to run premium in my '79... then as I got thinking about it... with a lousy 8.2:1 compression (for NA car) it shouldn't need premium.... so I use regular, and every once in a while fill up with Sunoco Ultra 93... even under the most demanding driving, the enigne never pings or anything... stock 425 runs fine on 87.... my '93 requires premium, dosn't ahve a knock sensor either... plus we advanced the timing a little... that car has never seen anything but premium sicne I owned it (don't know about it's history... I would say form everything, it always had premium) Sunoco Ultra 93 is what it likes best....
All in all, use what the owners manual says to use.... most forced induction or high performance enignes require premium... IIRC the 4banger in the Sentra SE-R needs premium as it is similar in design to a race enigne... just like the NorthStar....
... but be kind to the N*, give it premium gas, becuase it is a grerat engine in a luxury car, and it'll treat you great for years to come...