Way to go offering bad info JMHM17.
Not sure on the intercooler part, I cant see subaru rotating the turbo slightly to accommodate for a bigger intercooler.
Intercoolers do not interchange.
the difference between the 2 turbos is mainly the wastegate to hold boost better, also the dimensions are very very slightly different.
No good info here.
The STi internals are not different other than the pistons which are domed more but only slightly. Between the 2 motors one is no stronger than the other as they both have the same issues with ringlands (as far as pistons go). the big difference in the STi motors are their heads, they flow much better than the stock WRX heads, but I have been told that modded ej255 heads vs modded ej257 heads the 255 heads flow much better.
The pistons are not domed more as they are lower compression. Maybe inverted dome?
2011-2012 wrx vs sti is very minimal. The tranny and suspention is what you pay for, as for power, a pro tune on a wrx will get you the same power as a STOCK STi, along with some simple bolt ons.
Many WRX's have been dyno'd to have very similar peak HP and TQ outputs stock. On the STI you also get "upgraded" diffs, Brembo brakes, and 18x8.5" wheels.
My 2 pennies worth.