A few questions if you don't mind... how big is your room, is it mostly HT or a movie/music mix, if music how loud do you like to play and what kind 'o music ?

Most people here will try to talk you out of ceiling mounted surrounds, for some very good reasons

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8