I installed Focals (entry level) in my base model 2012 and it made a big improvement., however since the Stang has 5x7 (6x8) the bass is somewhat lacking. A spkr level input powered sub makes a huge differance but I haven't done that yet. The base model does NOT have pre-outs so you would have to get a spkr level input amp...unless you are adding a sub I wouldn't. The OEM's are some of the worse speakers I've heard in years. Updating all 4 is an afternoon and $150-300 well spent.
2012 V6 with suspension, shifting, stopping and sound mods.