Which keystone should I take on Malzahar and Vladimir? (I am speaking of the new runes)

Now that Deathfire Touch has been removed, I don't know what should I take on Malzahar. Scorch is the closest thing that there is to Deathfire Touch on the new runes. The problem is that it is not a keystone, it deals a fixed amount of damage that doesn't scale with AP or AD at all, and has a cooldown, It also doesn't seem worth taking over Gathering Storm. Will Arcane Comet be a good choice? I don't really know but it seems that this mastery has synergy with champions that have hard CC (Malzahar happens to have his ult). I also have thougth of taking Predator (it may seem weird but the movement speed active seems appealing).

As for Vladimir I don't really know what to take. Electrocute seems to be the closest thing that has synergy with him. Phase Rush, which is the new version of Stormraider's Surge, is harder to proc and only gives slow resistance to melee champions now. So it doesn't seem to be that good for Vlad anymore. The other old keystone that was amazing for Vlad was Deathfire Touch and, as you know, there is no replacement in the new keystones for Deathfire Touch. Speaking of which, I will really miss the movement speed quintessences for Vlad, because his base movement speed is so low.