Since you already have a JR, I suggest staying with JR. That way the equipment you already have will be useable and the 4 channel you can use as a buddy box. JR makes some very nice computer radios. I would still check out the channels though, a couple of crystals now will be less expensive than a bunch of them later if you decide to change channels.

As for PCM: The BIG thing with PCM is the fail safe. You program the receiver so that the plane does a certain thing in case of loss of signal. This is frequently reducing the engine to idle, leveling the plane and haveing the plane fly in a circle.

IMHO, unless you are in an area that has a lot of interference or you have a several thousand dollar plane in the air, it isn't worth the money. In almost 4 years of flying (this time ) I have seen 2 planes get "hits" (interference) and one plane get accidently "shot down" when someone else on the same channel turned on their radio WITHOUT CHECKING THE FREQUENCY BOARD OR PUTING UP THEIR FREQUENCY FLAG FIRST. They did pay to replace the plane/damaged equipment. Personally, I have never taken a hit (that I am aware of) or been shot down (I am one of two people on my channel).