By splitting your stay, you can squeeze in one more night and make it six - 3 GF and 3 BWI. You have the perfect opportunity to have it all. Three night at GF and you can do MK and AK, eat at Narcoosies and Chef Mickeys oh, and don't forget O'Hana's! Then three nights at BWI and then do EPCOT and MGM and allllllll the wonderful places to see (and eat at!) in World Showcase. You are not being selfish...as a matter of fact you would be showing your sis the best "the world" has to offer. Split stays are fun and a great answer to "should-I; shouldn't-I". Just MHO...