bigger or smaller enclosure

Larger box = lower bass response, yes.  More SPL, no, not that you would notice given what you said.  But you would probably have better SQ with the larger size given by the manufacturer.

With very LARGE differences in volume, say comparing 1.25 to 5 cu ft., the larger size will be more efficient and will make a noticeable difference in how the power is applied.  Or also in the case of small sealed vs. larger ported., the smaller sealed would need more power to achieve loudness and so can seem to be inefficient (not loud enough) if there isn't enough power available to give it what it wants.

Best thing for you to do is to pull out the woofer and fill the box with polyfil to create the impression of a larger volume.  You can cheat up 10-30% this way.