XPS 8900 for Full HD video editing?
For editing, I would definitely get a desktop PC, and a custom built one at that, not one from the shelf, as the latter will always be more expensive. Also, this way you only have to pay for the parts you need and can avoid bottlenecks. For example, the PC you mentioned doesn't have an SSD, so hard drive speed will be a limiting factor. Also, the GPU is sub-par compared to the CPU. 

Here's what I would recommend, should be doable with 1000 $ (Look out for assembling fees, some dealers will charge you up to 100 bucks, some will do it for 20. You could also do it yourself if you are confident enough):


An i7-processor. Since you should be getting a GPU anyway, you can get a Xeon E3 processor instead (basically an i7 without an integrated graphics unit, it's slightly cheaper). For example, I have the Xeon E3 V1231 v3.
An nVidia GPU with CUDA support. You could get a GTX 970, even though they are somewhat outdated. Alternatively, you could wait for the new Pascal architecture cards, however those will be much more expensive at launch. Alternatively, you could get an AMD R9 390, which only supports OpenCL but might be ever so slightly more powerful than the GTX 970.
A cheap HDD for storage as well as an SSD for fast editing. You don't need a Samsung Evo, it's a myth that those are better than the cheaper brands. For example, I have a 250GB Crucial BX100 and it's working perfectly fine.
At least 16 GB RAM.


It's important that you compare prices and different retailers.