I have the 4100 that you have listed and I love it. I was mainly interested in touch screen (which is great by the way) and the I-pod interface (and it is also great). Read Amazon.com's reviews and you will see pros and cons to it (you can get it through EB Electronics at amazon, thats where i got mine). I cant speak to the other HU. Send me your email and I will send you a word file on how to take the HU out, and a few wiring diagrams.
craigadean@yahoo.com One of the cons listed on Amazon for the 4100 was about the clock being in military time....They must have fixed that issue b/c mine is 12 hour time. I have the PAC-SWI steering control and was able to maintain volumes, tracks, and media buttons (media toggles through sources: ie sirius, ipod, radio, telephone.....). I was happy with that and didnt try to gain any other buttons. You can call PAC's customer service and they will tell you what the unit can actually do. The wiring harness that ford uses is a 24 pin harness that will run you about 25 bucks. There are two other harnesses that plug into the factory HU that I didnt use. You will have to do additional research to find a "mute" wire to silence your system when you are backing up(If you figure that out, let me know)I didnt mind losing the mute b/c the backup alarm still worked. . I also have the bluetooth adapter and the sirius satellite all connected to my system. Take a look at my mods, I have all the stuff listed.