The more CCA means the battery has the guts to crank a poorly-starting engine at 0*F for a longer period of time than a battery with fewer CCAs. No more, no less. Might make the starter spin a bit faster for easier starting, than a 650CCA battery might, but not over-power the electrical system. Seems like the CCA spec replaced the "Minutes of reserve" cranking power ratings prior to it? Is the pricing local, regionial, or national?
Re-read the description of the battery on the Interstate website. Is it a "deep cycle" battery for diesel engines or a trolling motor battery for a fishing boat? Free-replacement warranty period, too.
IT COULD well be that the particular batteries are near the end of their "Need to be sold by" period, too!!
A battery that size might be good for a drag racer car, rear-mounted battery, to run a maxi-spark ignition system, data logging system, high-volume electric fuel pump, etc. Charging it between races.
ONE thing it would do is allow an engine to run on a failing/failed alternator for a longer time before the alternator is replaced. Might also be a help on an aftermarket EFI system.
Just some thoughts and observations,
CBODY67