Dell XPS8500, Windows 7 (64bit), Intel i7 processor, 16GB Ram, 2TB hard drive and at least AMD Radeon HD7550 graphics card. Dell is still offering Windows 7 for now. Your Photoshop Elements 11 and your Nik software will run just fine. Buy all the RAM you can get. 4GB is not enough.
I run the system just described and it runs Photoshop CS6 and the Nik software like a champ.