TBH, unless your sub is much farther away than your speakers and your sub isn't noticeably distorting/compressing, then your single f110 should be sufficient for your speakers. Adding another f110 can smooth the in-room response (a valid reason for adding another identical sub) and will give you even more output (which you might never use).
IMHO, going for the more expensive sub is a waste of money (and, again IMHO, if your in-room response is "smooth enough", then buying another of any sub might be a waste of money).
But, if you do add another sub, then make it another f110.
You say you're satisfied with your system, so things could be worse.
People can expect too much from an upgrade/addition (expecting the same increase they received when they went from none to one) and are severely disappointed when they hear what they get (and those JL aren't cheap).
If your dealer will loan you an f110, you could then hear what you'll get for that extra money at very little risk.