Moving from a FMIC to a TMIC you will be looking at 500-700rpm of lag on the stock turbo (or stock sized turbos, 20g, dom 1.5 ect.), then add onto that the added throttle delay and the benefits quickly start to disappear. If you are doing drag racing or even road course this will not be so much of an issue as the RPMs tend to stay up there the whole time and your foot is planted on the throttle most of the time. Although on the road course you would have to learn to throttle before you usually would with a TMIC, other wise you will find your self not accelerating out of the turn like you should.
When ever you add more piping you are losing efficiency. You are forcing the turbo to compress more and more area, thus making it work harder, for longer. While this might not be so much of an issue with larger turbos (Dom3, FP black, ect.) with stock sized turbos where people are constantly maxing out the compressor map on the TMIC, moving to a FMIC will not help performance. What you will be doing then is forcing the compressor to work outside of the efficiency range. This means the turbo will be spinning faster, heating up more, and pumping out warm air. Yes the air is compressed down to 25psi but the density of it is crap. Yes the FMIC will cool this charge down so it is not detonating the motor (hopefully that is), the problem is you will have less air mass coming in at that higher PSI then you would at a lower cooler psi, this is why turbo manufacturers spend so much money into developing turbos with the largest compressor maps possible; and also why you don't see people pushing 35 or 40psi on the stock turbo, it's pointless. All you are accomplishing is turning the stock unit into a hair dryer. I wont even go into the damage you will cause to the unit by forcing it to work at that higher psi either but needless to say spinning a turbo up to 200k rpm daily when it was only designed to be used at 120k rpm is not part of the recipe for longevity.
Something else to consider with a FMIC setup is the hood scoop. The scoop sucks in air and creates a low pressure zone. This then is sucked out and under the car. With the hood scoop installed you are dramatically limiting the amount of air flow you push through the front as the front of the engine tunes into a high pressure zone, forcing air away from it, meaning you get less efficiency (not positive about the zones but pretty sure I got it right). So basically if you are thinking of cost wise you need to add in the cost of a hood scoop delete, either a Impreza RS hood or a delete plate. Problem is most people would not even consider the air flow and just toss a FMIC on and call it good with the stock scoop still on and sucking in air.
