Regular is better than premium, for our bikes.
An engine designed for a high octane gasoline will experience per-ignition or detonation when run on a low octane gasoline... A lot of cars and a few bikes have knock sensors to detect early signs of pre-ignition, and retard the intake timing to compensate, but in doing so will suffer a noticeable loss of power and fuel economy. Vehicles that take premium and do not have knock sensors will suffer damage, and reduced performance.
However, octane enhancers tend to increase the temperature required to ignite the fuel, slow the flame propagation speed, and don't tend to burn as well as more pure regular fuels.
Since the GS runs just fine on regular, you're paying more money for lower performing fuel. If you want to take advantage of premium fuels, you could advance your ignition timing, or install higher compression pistons. In doing so, you'll generate better power, and/or better fuel efficiency.
Premium fuels may have extra detergents such as Techron or V-power, but those don't actually benefit performance unless your engine is in need of a very good cleaning.
