I just fitted an 06/07 sti cluster to my 06 wrx. Had to modify 1 plug to fit and cut 1 wire to stop constant beep. Everything works perfect except i have r.diff temp light on constant but seeing as the car doesn't have the sensor anyway I'm not fussed with it.

From the hours of research i generally read that the same year sti cluster will have less issues when fitted to the same year wrx. You will have to modify slightly. Very unlikely just will be direct plug and play. But then again some people had issues that others didn't.