If I can chuck my two-penneth in - I was involved in the construction of a fixed base simulator based on the 737-800. We used a shell of a real scrapped 737-200 and retrofitted a glass-cockpit, using our in-house software for display. FS9 was as the visual model and we had a 737 add-on (I can't remember which one) as the flight model.
There is a video of the sim here:
https://www.youtube.com/watch?v=nUvYSa5VvKI
I had extensive time 'flying' this device and also had 2 hours in the same year on a real 737-800 Level D sim.
The two were obviously different, the biggest difference being the motion and the 'feel' of inertia on the Level D but the differences were not outlandish. I learned to fly on the fixed base sim and was able to handle the level D perfectly well.
On a separate note, I am planning to build a simple home sim and came across this thread after a search on Prepar3D - which is what I am planning to use as the sim. I just wondered if anyone has any experience with this sim product and can give any accounts of their experiences?