I've been going back and forth in my mind so much now trying to decide between the 20 inch imac models. I will be using it to edit video in iMovie, backup DVDs, manage/edit photos, play around in garageband with my electric guitar, and internet. No gaming or using professional apps. Which one is right for me? How much of a real world difference will I notice by having a slightly better graphics card and .4 more GHz of cpu power?