Loaded question that has been discussed MANY times before. No, it doesn't REQUIRE premium to run, but the owner's manual STRONGLY recommends premium. If anything less is used, GM advises no aggressive driving until premium is obtained. Why would anyone have a 556 HP engine and not use the recommended fuel?
Depends on what you mean by "premium." In the high plains and mountain states "premium gasoline" ranges from 89 (mountain) to 91 (high plains) octane. In the coastal region where I live, premium is 93 octane. The owner's manual for the CTS-V recommends a minimum of 91 octane. Since 91 is not available where I live, I use 93 (the next step down is 89 octane). If 91 were available, I would use it. The Top Tier gasolines have additional cleaning agents (supposedly). I try to use them when they are available.