I seem to have things quite stable and fluid.
X-plane is absolutely gorgeous at nightime as I did a test flight out of Heathrow over London and the sky is actually dark and the ground effects lighting is simply stunning.
The significant downside I can see thus far is that despite loading an enhanced EGLL the terminals and taxiways really don't match up well with reality so online jet or turboprop flight between significant airfields may be an issue as taxi/docking accurately is fairly important. And I am not wild about the default aircraft beyond the Piper (which actually flies well and has a decent virtual cockpit) and I find the downloaded Twin Otter rather bleah (although the flight model is about the same as ours under FSX.
I am going to research a strong payware model (likely the MU-2 or one of the PC-12's) and have a go. I will also get the freeware x737 and see how that model works depsite the lack of a 2D pit just to get a proper feel for a proper jet aircraft in the sim.
It seems to me so far that where Xplane utterly shines is in the area of prop/turboprop flight and the sim fluidity
Just as a side note I have also just ordered and will be installing FS9

. I also got the PMDG 737 6/7/8/900 package for a song from Amazon at the same time. I was reluctant to do this but as my F1 ATR, QW757, FSC, and REX all came with installers for FS9 what the heck. Why not have at least one sim that can run at max fidelity given my current hardware

.
I can easily see myself using FSX for the Twin Otter/PC-12 as those planes are just awesome and smooth....as is the QW 757 for the most part, the heavy metal stuff like PMDG on FS9, and the MU-2/PC-12 under X-plane for when FSX/FS9 begins to become irritating.
I'm still in the process of getting the controls sussed out and mapped properly to my stick/HOTAS. And how the heck can I disable or change the assignment of the scroll wheel on my mouse away from throttle control!
More rambles as I experiment some more. I am getting tempted to check out Mars lol.