I will be purchasing the 27 inch imac for avid and after effects. I'm sure I need 24 or 32 gigs of ram. How come 24 gigs isn't an option to upgrade? Also, if I'm going third party....it'd still like to stay with quality. There are tons of different companies making ram and each company has different types? If I were to upgrade with a third party, is going 24 an option? And which company should I go with for the ram?