If you have about $500 sitting around and a lap top, you too can access your ECM and change things around to your heart's content (not a good idea actually unless you really know what you are doing). Just go to this site:
http://www.hptuners.com/
I have a 2009 Pontiac G8GT with the L76 6.0 V8 and the A6. I bought HPTuners for my 2005 GTO and had addtional licenses so when I traded the GTO in on the G8 last month, I was able to license the G8 and download the ECM data. I then made some minor changes like turning off the DOD (I did not care for the roughness, even though it was mild) and reflashed the ECM.
Anyway, just like the L99, the L76 also has high and low octane tables. This is what the HPTuners help section says about them:
Main Spark Tables
The VCM constantly looks up both High Octane and Low Octane spark tables and interpolates a value between the two tables based on the current Knock Learn factor. If the engine has been operating for a moderate time without any Knock Retard then Knock Learn is zero and the interpolation favors the High Octane table, if Knock has been detected then the interpolation will move towards the Low Octane table. During MAF failure the Knock Learn is set to maximum and the Low Octane table is used (HP Tuners speed density enhancements allow both spark tables to function).
By the way, the L76 is a premium fuel
recommended engine and the quick reference guide says the engine will run on regular but run better on premium, obviously because of the different octane tables. On the other hand, the LS2 in my GTO was a premium fuel
required engine and did not have different spark tables. I did not notice but did anyone confirm whether the LS3 has two octane tables?