I don't think we have ever had a thread that has stayed on topic for very long. Being that this thread was created more than a year ago, I think it is a safe bet to assume that it going off topic for a bit wouldn't upset the Op.
I didn't even notice how old the thread was
Have you ran a standard c/o before and if so, I'm assuming it's night and day difference?
Yes, I have a little experience with coil-overs. I couldn’t say that it’s a night and day difference, but compression is far better/smoother in the IBP. As I’m sure you are aware, terrain, vehicle weight, and shock stroke are all factors that determine handling characteristics. My Jeep weighed in at just over 5k in race trim, and with a class limitation of a 14” stroke shock, compromises had to be made. I chose to use a 12" shock to avoid driveline bind issues with the 1350 u-joints. We gave up speed in the extremely rough terrain, but gained speed in moderate terrain and rock sections. Budget is always a concern, and these work very well given their price point. Coil carriers and external bypasses would certainly work better in this class, but this Jeep is still my trail rig. I wanted to be competitive, properly market our advertisers products, but still have a trail Jeep after the race.
Is tuning a pain or pretty easy?
They tune like any other shock, but we felt we had what we needed right out of the box from King and chose not to further tune them. (more info on that is in the article referenced below)
Any issue with excessive fade on them?
The terrain was so rough in many areas of the desert lap that we kept our speed way down (25 MPH in some areas) to avoid crashing into the bumpstops. In the areas that we did go fast, I didn't notice any fade issues.
Do they use a fullsize 2.5" piston or are they sleeved down to something smaller?
Looking at the photo in the link below, I assume it is a 2.5” piston.
And, here is a link that discusses our thought after our first, and only, testing session before the race.