Old School,
I respectfully disagree. Unless you are using the second, high CCA battery, as your primary "starting" battery, "bigger CCA" is seldom the optimal choice. Auto starting batteries are typically rated in CCA, "cold cranking amps" where high amp output is had by using thin battery plates to maximize surface area. This is a trade-off, powerful yes, but the battery is designed to output this high power for 15 seconds to start a car engine at about zero F.
Many want their AUX battery to deliver more moderate power output for longer periods. Operating a winch or accessories, even with engine off, is where the deep cycle or storage battery, with its thicker plates, shines. The storage battery will be rated in amp hour (AH) capacity. This battery is better for arduous winch pulls and longer periods operating accessories with or without the engine running.
This is not to say one can't swap one battery type for the other or ignore all of the above, but for optimum performance and long life . . . each battery type is engineered for a purpose.