higher or lower frequency for spl?

Which is better for higher SPL numbers, higher or lower hertz (25 or 45) hearing mixed opinions about this

It is harder to achieve higher numbers at lower frequencies.  45 will be the easier option.

Its a 03 exscursion, behind the 3rd row, currently running about 6 cubes per sub, they are for now the power acustik fubars and running a 2500 mono D to them at 1 ohm, currently hitting 141.7 with the square ports that are 18 inches wide 3 inches tall and run 35 inches into the box (down the depth of the box, turn and stop n the middle of the sub). the box is about 40 wide 28 deep and 25 tall, split down the center  and the ports are on the face, i want to try and get around a 144-148 range, i know it can be done with these sub/amp setup, i just need to tune it right