The "7" is one heat range hotter than the original and the "ES" is a standard electrode material where as the "EG" is platinum I believe (going from memory here). The "R" means it is a resistor plug which helps eliminate radio and other electronic interference. Like Lankydoug said, some guys will use a hotter plug to try and avoid jetting a bike properly or cover up other mechanical issues, but it should run best with the factory recommended heat range unless heavily modified. Here is a link to a good explanation of heat ranges:
http://www.championsparkplugs.com/ch...?kw=Heat+range
Wes.