Don't go bigger with the PowerMax as it does not hold voltage once the set point is hit. Once it hits 14.6 PowerMax drops down to 13.6 and you are back to slow charging. I think BFL13 measured about 75% charged when it steps down. The effect of a smaller unit will kick down at a higher percentage. Think 35a or 45a max with PowerMax and two batteries.
IOTA and Progressive hold voltage 14.2+ for an extended period and might serve you better. Going more amps with these is fine, especially the Progressive. Check your battery connection size before you go over 60 amps.