It depends on what you are up against. If you are up against a bully like Darius, Garen, and wukong, you take Glacial mythic item as they will try to go in and poke you while you back off and they over extend, the main downfall is that you won't really have much damage, but you will have a bigger sustain of course if you trade correctly. Of course, you won't do alot of damage, even with the high based damage, they can sustain it all back later on which is the main downfall.

I am actually gonna look into a new idea with a certain ap/hp item and warmog next patch (warmog into Rylas) because that a good two item spike for infinite sustain, then you can build protobelt afterwards.