IIRC seven is the highest level we can get, at least in the course of the game. Theoretically there's bigger, but that's more of an abstract beyond what works in the Wake. Like, Names and Hours should totally have higher levels, but they only use a fraction of their power when summoned for reasons. Also it won't be a sacrament, exactly, but Bird did say at some point that the breakpoints for unique powers are 3, 5, and 7. They're more special somehow.
we at least know the rewards for each level up to 5.
lvl 0: +1 to appropriate roll
lvl 1: another +4 to appropriate roll
lvl 2: another +5 to appropriate roll, and +1 to an appropriate stat (honestly I always thought that was a bit too low though. It should be higher!)
lvl 3: another +5 to appropriate roll, and a "Realization" power. From alchemical reagents, to Risen-making, to touch-reading/Psychometry, and so on. Most of them are objectively pretty useful, if a bit niche.
lvl 4: another + 5 to appropriate roll, AND a re-roll on that lore once per turn on the most beneficial roll (Except Edge. That's one reroll every 6 rounds of combat. Weirdly enough it doesn't apply outside of combat)
lvl 5:
presumably another +5 and the Sacrament power, which will presumably be far stronger than the Realization. for SH for example I'm expecting something along the lines of being able to use the parallel-history-sight to help in picking our actions, maybe by giving hints of potential results.
lvl 6 and 7: who knows. Presumably 7 is some even bigger power. I kinda expect lvl 6 might allow us to call down influences at will on our own, like our Names can do.
Hmm, speaking of the Mansus, what do people want to do with the feee exploration action next turn? Personally I'm hoping to keep exploring the Stairs, since there's pretty much the last place to check, except for the new Ash. Well, unless we want to take a shot at the Church depths…
well, we'll want to see what our situation is with Luna first, but I'm down for the church.
And once the SH Sacrament is done, we can check the Tower!