Adam,
I appreciate what you're saying. I spose the key to my seemingly successful use of this approach, over some 25 years boating ( 42' diesel, downeast style) is that I always use batteries of the same age and size, same holds true in the 110. In fact the date code on the 2 in the 110 are the same. I am not a spiral cell user, and those I know who do, really don't boast the greatest success stories, perhaps as they may be improperly applied. There is one I might try, a little known Blue top Optima, which has the best charcateristics of both the red and yellow. The two 800cca in my 110 are Interstate, a common aftermarket battery used throughout the US, and I doubt any Sears Diehard is as good. Mine are going on 4 years now, and I do a fair bit of winching, either with the Warn 9000 up front, or the Ramsey worm drive 12K on the rear. I have a 130 amp alternator, and the voltmeter never dips below 14 with all the lights lit. I alternate, weekly or thereabouts between Batt1 and Batt2, rarely is the switch in the 'both' position.