Unlike the newer WRXs, GC8 ECUs will not crack a spaz at moderate intake and exhaust mods. A FMIC running on your standard
ECU will be fine, and you will see some small but noticeable gains from it.
Also, you dont have to go out and spend thousands on a new
ECU. Take a look at the secondhand market. REXNET is a good place to go for cheap 2nd hand ECUs.
Also consider The Power FC as they are still readily available for later GC8s and are easily the best back for your buck after market
ECU out there. They usually cost around $1200 new $1000 used including the hand controller. And lots of Suby workshops tune them. A power FC tune will probably cost in the region of $500.
Also if you have a my00 GC8 you can actually get a ECUTEK tune reflash. I have heard it was done on only a handful of my00 GC8s. But a Power FC is still be a better option as the cost is not much more and the Power FC
ECU is a better
ECU than a re-flashed stock
ECU.