As mentioned already, IC is not essential with Stage 2+, especially during the winter. However, during the summer months after a few WOT runs, my car would run noticeably slower and if I were to go down the route again I would opt for a Twintercooler or similar (just wasn't worth while for me, as the car was going soon after).
On a 1/4 mile run for example, if 2 x Stage 2+ identical cars were to run against each other and one had uprated FMIC compared to the other having OEM. I would say there would be bog all difference (mine was certainly quick enough for minimal mods
). If both cars were on a track day though and were continuously being ragged round the track. The OEM cooler'd car would soon be struggling after a couple of laps.
Depends what your circumstances are really and how long you intend on keeping the car. Even with a oem cooler'd car, it will be a seriously quick hatchback!!!!
This is better scaled plot of the same RR run. This was before I changed the Dbilas intake for a EVOMS.. (which was noticeably better IMO, just never got it on the rollers again to see
).
In the winter it makes next to no difference IMO. I logged mine in 5/6oC AT and even when knocking the timing upto 8, I got next to no timing pull on continuous 3rd and 4th gear WOT runs..