not that much different than your jamis, except that your jamis has better geometry..
If you want to spend the amount of money that it takes to get something that is similer to your jamis and possibly better, the only ellsworth contender would be the Moment. The Id's bottom bracket height is about 15". To put that in perspective, the BB height for a turner 5 spot is 13.3 and a foes fxr is also 13.3. To put it simply, the ID is a freak of nature.
Ellsworth bikes aren't the end-all, they aren't even any better than many big-name bike IMO, and at the least the warrenty with companies like specialized and giant is infinitely better (there is no 10 year warrenty for ellsworth, if they change one aspect of the bike like the chainstay, then it is not consiered to be the same model year that your bike is, and your 10 year "warrenty" is invalid).
If you were looking for a nice XC bike like the Ellsworth Truth, then that might make a good bike for you, as it has for many people. There are some things that ellsworth makes that are pretty nice and work pretty well (when not talking about the warrenty practices). To use someone elses words, the id is a very confused bike. It's not very durable (it was originally marketed as a full on freeride bike, they've now backed off on that though), it has "freakish geometry" compared to similer bikes, and again, it's a horst link bike, just like your Jamis. It isn't going to ride dramatically different, you'd be better off putting a romic on your jamis if you do not already have one, or a 5th element/manitou swinger.
The isis (and joker) are simple single pivot bikes. Nothing special except that "ellsworth" name on the side. If you want a single pivot, get one from a company that does it right, like foes. For about 1400 you can get one with a romic or vanilla RL shock, it has a low pivot, "propedal" or the romic to help with the pedaling and counter that low pivot (curnutt if you have the money), active suspension from the low pivot so no chain extention problems, stiffening linkage that keeps it ultra-stiff, and awesome geometry. My FXR is simply better in every way, AND it can be had for about the same amount of money or less. I wouldn't say that you have to buy an FXR, but in the same line of thinking-there are other good choices out there.
If someone was saying that they wanted an ellsworth Truth for XC riding, I wouldn't post or say anything here. It's a good bike for XC and while fairly expensive, it's not a bad bike or anything. When you look at the Id though, there are some pretty big drawbacks to the handling of the bike, and it is not that much different than your current bike. When you look at the Isis, the difference in performance and advanages is even more dramatic when compared to your current bike.
If you want an ellsworth, consider the moment, it has "realistic" geometry, if you get the Id is questionable if there will be any improvement over your current bike, and it is easily arguable that it will be worse. If you get the Isis, it will be worse.