As Speak2Mountain said, RL is overkill for this application. Actually, it is overkill for most normal cars and driving conditions. Any Dexos1 oil will be fine for the CTS in non-race situations.
However, if your car consumes oil like my 07 CTS did (1qt/1k miles), it may be good to switch to HM. I recently switched to Pennzoil Plat HM and the consumption is virtually gone. It now uses about .5qt/3k miles. Pennzoil Plat HM is not Dexos1 certified, in case that matters to you.