As an avid Guinness drinker (as well as a Harp's and Smithwick's drinker, same family) I can say I've never noticed a difference in my ability to get inebrieted. It is definitely harder to get plowed on Guinness simply because it is like drinking liquid bread. I recommend you try Smithwick's or Harp's for that. As for the alcohol content, it varies from country to country. Guinness changes it for taste.
Now I'm thirsty
