Good question is a 34 vs. a 35 series battery, the 35 has 720 CCA (cold cranking amps) the 34 has 800 CCA. there is also a slight difference in shape, however this is of no concern since neither is the exact same size as factory. The 34 series has a higher reserve capacity also. There is no reason to run a 35 over a 34 unless you are worried about the 6.2lbs in extra weight.
massive thread necro via google but anyways just to make sure, this is a drop in replacement? The current optima battery I have is way to small and actually slips out of the battery connections every few months which sucks.