The heads on a subaru doesn't flow well stock, the stock exhaust and intake manifolds suck. I've seen fast spool and big numbers out of stock 4g63s. They designed their heads(as well as IM and EM) so efficiently stock they make gobs of power quickly with small displacement.
Personally I'm coming to the conclusion that having an H4 is like having a rx7/rx8.. it's different and sounds different. But the Evo8/9/10 is and still is the better car even with less displacement. Corner weights can take care of the inline/transverse style engine layout. The Evo transmission 5spd are stronger than WRX 5 spd. If Mitsubishi started putting a variant of the 2.4L world engine in the Evo it will be number 1, unless your then choosing based on looks and sound of the car.