good thread, you've been keeping up on your research.
for anyone looking at a FMI it should be noted that on a stock set up, they are just about useless, maybe a gain of 1-2 horsepower. however, once mated with a tune they become very effective as the air coming in is closer matched to the cooling provided by the intercooler. Adding other bolt-ons only helps this.
The main reason i'm going for the FMI is because of the heat soak, it annoys the hell out of me, i can only accelerate a a few times in a row before i feel like i'm driving a truck. I had a lot of experience with this with a previous car i owned, there are a few tricks to avoid it (still had an uprated intercooler there too), however the ecu is a little more advanced in these cars, and it really cuts the power
if you want the biggest gain on the stock car (no tune and tuned), it's the catless downpipes followed by a downpipe back exhaust system. The catalytic converters are huge power drains on the car. when they were first invented, it was commonly believed that 1 catalytic converter robbed 10% of a cars power, it isn't that extreme anymore since the technology has advanced, but it should be noted that our cars come with 4. Just getting rid of 2 of them will make a world of difference.
Opened up flow in an exhaust system can result in quicker turbo spooling times, sometimes allowing the car to hold power longer, as well as put down bigger numbers.
con (matter of opinion) is the car will be a little louder.