Eldrazi Conscription
I prefer such abilities to trigger during the upkeep step, because nearly every other ability triggers during that step, and, as far as I am aware, there are very few abilities that trigger during the draw step, apart from additional card drawing, so everything would be easier and more uniform if the upkeep step was the universal (or near universal) step during which abilities triggered
There's also a handful of other cards that increases power, mostly equipments like Champion's Helm, but most of these bump the power by about 2 and not enough to get most creatures to 7+ power
You'll be able to indiscriminately dish out damage thanks to inclusions like Persistent Constrictor and Harsh Mentor
Reckoner Bankbuster You probably know Reckoner Bankbuster from its long, banworthy stint in Standard, though I encourage players to test it out in Commander too, especially in decks seeking more card advantage