Endless debate: monitor + sub vs floorstanding

Have made a simple system with Peachtree Inova and Proac Sig 8 Tablettes on sand filled stands. Lovely sound I am quite pleased with though I'm considering either supplementing my beloved Tablettes with a sub bass (most likely the new Rel T5) OR grabbing a pair of full range floorstanders (likely used Proac as well).

Any thoughts on the relative merits of the two setups in terms of expression, detail, dynamic spectrum, musicality and also flexibility? Intuitively, it seems I may have more opportunities to play with and fine-tune the experience using Tabletttes plus sub.

I realize there is probably no perfect answer here. Unfortunately, my opportunities for a good side by side listening comparison of the two systems is pretty much nil.
A pair of capable monitors and multiple subs will have less peaks and nulls in the bass region.
John Marks has some interesting observations on this topic here:

Interesting article. I knew that there seemed to be a two-way bookshelf camp, but I'd never read an argument for the point of view.
I'd attribute your ProAc dealer's remarks to the fact that he's a ProAc dealer.
IME, properly set up subs are a revelation. Of course, that part about properly set up is important. Few full range speakers can produce clean measured response in the deep bass ala Rythmik, JL, SVS. Further, properly placed subs will create much smoother bass response, although this can also be achieved with room correction like Audyssey.

Either way, uncorrected bass response from a floor stander out in the room just doesn't cut it for me anymore.

I'd stay away from REL at all costs. If have any problems with your sub you have to deal with Sumiko and they are a bunch of azzholes.