you probably wouldn't be able to get everything out of the 1500 anyway without any electrical upgrades. But I would say at 14 plus volts you could do a solid 1650-1700. Which verse your probably 1200-1250 would make a difference.
i do have a big batt up front,big 3 with 0 awg wire and a 110 amp factory alt.and if it will make a difference,then i guess ill get the one i seen on ebay thats rated at 1635 .i have seen where some were rated at a little over 1800.sure wish i could find one of those.