I've used a 5-3-2 (DL-DCx3-DR/MCx3/STx2) in the last moments to keep an advantageous score, generally when I've played originally a defensive 3-5-2 (DCx3/WBL-WBR/MCx3/STx2). I've done those seeing only key players, so don't have the proper knowledge of it real working to make a detailed post (I will soon play one watching all and then I'll tell you).
The DCs are set to keep back the ones at the sides in the most defensive setting among the team (not less than -8 in mentality), the central as defensive but set to go forward mixed. The wing backs have the team mentality that uses to be attacking and some times normal. Alike to the defense line, the midfielders at the sides are set to be attacking (one of them is the playmaker) and the central is to take a defensive task, though if receiving the ball may run forward with it. The play will go mixed throrough the whole width of the field and set to wide (have to note up to now my field was narrow and short and most of the matches were played in such fields). Defensive line pumped up.
My defenders are fairly good at tackling, heading and in the least not slow. They do work rather well, getting a fair share of off sides, able to get to whoever would get behind and they seem to be effective at keeping the opposition at bay. My problems have been more in the lack of attacking efficiency, but a good part of that was some of my recent past failures at getting the tactics right, with strikers of not that much quality, however the attack wasn't that bad either, as I won a good share of matches and given trouble to some big teams.
It's by dragging the WBL/R to DL/R position how I made it into a 5-3-2, which keeps all the defensive power from 3-5-2, though losses capacity to make offsides by just a little and in the other hand losses much of the attacking potential.
So I would go for the three defenders rather than five, as attack is better, but that's from my experience not watching all the match and with several tactical problems.