That's... not really entirely correct. The octane suggestions are there for a reason, and it's not because GM is trying to screw you out of more money. This is a high performance car with a forced induction engine, not a Sentra. The car was tuned by GM to run on a MINIMUM of 91 octane. Running anything less than that causes the ECU to pull timing and at the point your car isn't running as well as it should be. Sure it's possible to run on 87 octane and not have detonation, if the conditions all line up. Cooler climate, no heat soak, no load on the engine, that sort of thing. But the ECU is still pulling timing at that point, even if it's not pinging.
In the OP's case, if he's forced to use 87 yes the car will survive if he drives it gently. That should be fine. That's different than using 87 for the span of the car's life. When you say "the car runs great", have you put it on a dyno to verify that? Have you checked to see how much timing has been pulled? I'm guessing your car is in a constant state of power loss because on 87 the ECU has to pull timing to prevent detonation. Your throttle response is not as good as it should be because of the retarded ignition timing and you're down horsepower.
If you want to cripple your car by running 87 all the time, that your choice - but DO NOT tell people it's "fine" or that there is "no harm" in doing it. That's bullshit. In a hot climate, an environment with a lot of hills or anything that adds heat to the cylinders, the ECU will not be able to retard timing enough to prevent detonation on 87 octane. Furthermore, light pinging is inaudible, so saying you can't hear it ping is irrelevant. You've probably been damaging your piston crowns the entire time you've been running 87, even if it's only light damage.
Why you would spend $70k on a super high performance car just to put 87 in it and cripple performance is beyond me, but it's your money. But you need to stop telling people there is "no harm" in using 87, because that's wrong. I live in the desert, what do you think would happen if I used 87 out here? It gets so hot out here I get heat soak just driving on the freeway, the ECU pulls timing even on 91 octane. And the CTS-V is more forgiving than a lot of higher-strung FI cars.
As I've said if you take it easy and you don't live in an oven, running 87 will work if you keep the engine load low. That is absolutely not the same thing as saying it's fine to use 87, or that there's no harm in using it. And besides, what are you saving, maybe $4 per fillup by using 87 instead of premium? You're gonna buy a $70k super high performance car and then try to save $4 per tank by using 87 which reduces power and throttle response and possibly causes detonation? To save $4? A cup of coffee at Starbucks costs more than that. You could have saved a whole lot more money by buying a Prius instead of a CTS-V, and THAT car is fine on 87. IMO the only conceivably acceptable reason to use 87 is for something like the OP's case where he can't find anything better and doesn't have a choice.