Just installed a kit from X-Factory on my 77S, could not be happier with the experience and results. Immediate throttle response and total control over the engine rpm/load range. Plus you have complete visibility of fuel/ignition operation with the data logging capability. Really nice being able to tune your engine from the drivers seat!
http://http://forums.pelicanparts.com/porsche-911-technical-forum/1005109-pmo-itb-aem-2-7l-install-notes.html