I am not criticising Barefaced, their 4 ohm cabs have two drivers, but you will get very little extra from your amp by going to 4 ohms, unless you do it with two drivers. Taking into account the extra power losses, a single 4ohm driver will only give you about 1dB extra. That is just noticeable so not really worth the trouble as you will not be able to double up on cabinets.
A good single 12" woofer cabinet would be a better bet in that adding a second Identical cab would, stacked vertically, give a real noticeable difference.