Hmm I have found It generally to be the other way in my experience. Most 12v batteries I see are hybrids of starting battery design, and they excel at high amp draws, as well as maintaining a higher operating voltage than golf cart batteries under high draw. Now that said I don't consider 30 amps all that high a draw, and I think golf cart batteries are well suited to that kind of duty.
Making a voltage table for your batteries under charge or discharge as you are doing is actually a more accurate way of testing their state of charge than rest voltage, as long as you have voltages lines for various amps.
Jim
