Won't disagree that Garmin makes the best GPS units for the personal market, I have the 60CSX with the new Sirf III chip. However, for a road naviagtion unit you do not need the accuracy that a 60CSX will render.
Road naviagation units are designed to track to the road, so even if my Garmin shows the Pioneer unit I have is about 20 feet off, the Pioneer still shows you on the correct road. You also do not require as many channels and WAAS capability for car units.
In addition, I don't believe Garmin makes a unit that integrates into the dash panel and is also a radio head unit.
Now to the original question; I'm going to guess the installation of either the Eclipse or the Pioneer AVIC units is about the same. Adapters are required for the Pioneer install, and I believe adapters are also required for the Eclipse install. The rear camera will have to have the wires run into the vehicle to the head unit.
