After more than 17 years - my red top Optima battery finally gave up the ghost. Looking at purchasing an Interstate battery from Costco (based on all the positive remarks about that brand of battery on this forum). My TR3A has been converted to Negative ground. Which size battery would be best - the 24 or the 27? Or, should I just go with the larger size battery (the 27) because it has greater cold cranking amps (810 versus 700)?