You can not go wrong with a catch can. It was my first mod on the Mustang.
Long story short: I was datalogging my previous '07 SRT8 Charger and could not figure out why the PCM was pulling timing (thus reducing power) at high rpm. I installed a catch can and, sure enough, my timing was rock steady. The oil coming in through the pcv system was contaminating the intake charge.
I didn't even mess around with the Mustang, JLT catch can installed on day 2 of ownership.
2011 Mustang GT Premium, 6spd, Brembo - 12.51 @ 115.53 mph on street tires
Gone but not forgotten: '07 SRT8 Charger, '04 STi, '01 Camaro SS
Life Member: Veterans of Foreign Wars