Yes, it should work in an '05 WRX, as far as I know.
ACT clutches are powerful and smooth. They don't chatter in the cold like Exedy clutches. I think you would be really happy with it installed, even with only lightweight pulleys. You'll feel the power you have MUCH better than with your OE clutch. There's nothing like going through the gears with a tight, snappy clutch. Very enjoyable.