Alright, now that I'm at my computer, I'll give you my thoughts.
I started with a spacer lift and FJ coils on the front of mine. I loved the improved ride, but unfortunately it was only in the front. The rear wasn't matched very well and it just felt awkward because the rear rode worse than the front. It was better than stock, it's just that when the front/rear isn't even it is much more noticeable.
After riding in a 4runner with the FJ swap and 5100's, I decided to go that route. I did 5100's and FJ coils on the front, and used the Bilstein HD's on the rear. The HD's, as mentioned, are the same valve rates as the 5100's so it should be a great match. After the swap, ride overall seemed to have improved (definitely in the front, everything I'm speaking of is about the rear). The rear now seems to bounce quite a bit. A good example is expansion joints in the highway. The front glides over it, nothing is felt. When the rear hits, it's felt and makes the bump feel ten times larger than the one the front went over. If I hit a speed bump at 15 mph or so, the front bounces but soaks it up very well, but the rear feels like it bounces off the ground. It's almost as if there's no shock back there, it's just a stiff ride. I had this issue before the swap, seems it's a little worse now though.
So, that led me to think it was the shocks. I then went through three other sets of shocks, thinking that the HD stocks were simply too stiff. My next choice was a set of Rancho RS9000XL's. I chose these because they have adjustable firmness. I could definitely tell a difference in ride quality when I adjusted them, but the bounce issue was still there, it didn't improve at all. I thought maybe even on the lowest setting they were too stiff, so I got a set of OEM FJ shocks. Same story with them. Last choice was a set of OEM non-xreas 4runner shocks. These are the softest of the ones I've tried, but still not much improvement at all in the bounce.
You may think I'm overplaying the bounce, but it's very noticeable and happens often. I don't think it's a related to ditching xreas, I think it is more about timing. I'm at over 150k miles, and I think my rear air system is on its way out. As soon as funds allow, I'm going to pull the bags and install some Toytec superflex coils with 5100 rears (for the added length over the HD's).
So, there's my experience with ditching xreas on a rear air equipped 4runner. It's been a rough road, a lot of money spent with little/no improvement (again, just in the rear). I still think this is limited to my 4runner and the system being worn, but thought it was worth sharing.
If you want to go this route, PM me and we'll work something out on the Bilstein HD rear shocks. I've got them laying around just taking up space, I think they *might* have 10k miles, no more than that.
