It's clear that the evolved form of Pokemon have a far higher CP cap (and it looks like minimum too) but it would also seem there is a difference between different Pokemon.
For example I have an Oddish at 184 CP which is at 50% of it's cap, and I also have a Ratata at 185 CP but it is far closer to its cap, around 90%.
Which Pokemon have the highest CP caps?
Best Answer
Table below in "Max Total CP" order.
(I included the table below so there is no need to jump to a new link, or incase the original is inaccessible.)
As you do powerups after finding a wild Pokemon, some multiple better, thus being stronger or top tier pokemon.
Multiple your character level by CP per Powerup (aka, multiplier) to see approximately how much their CP would go up.
Ndex is their Pokédex number