i have the same pc without any problems, although when i switch planes a lot or use the menu bar a bit too extensive, my FSX freezes, but since i also had this problem on my older pc, i say its an FSX bug. There are many topics about this and there is some on the internet with a solution to reduce this, google uiautomationcore.dll and you will find some of those.

don't worry about the brand dell.. some people have bad experience with some brands and one says dell is crap, others say its hp or apple or whatever brand they had problems with, but you cannot judge by it since you don't know how they used their pc.  I myself am an IT guy at a big worldwide company and we use Dell in the whole of Europe and hardly have any issues: servers, desktops, laptops, you name it.
Also, if Dell is that bad, why are they in the top worldwide selling brands.