Thank you for providing the specs. Indeed you should not be running into any FPS issues with that sort of rig. There's a few Let's Plays and general gameplay videos floating about the internet and you'll see that those FPS issues aren't present so I have to assume it's something more localized. Leave it with me and I'll see what I can find.
If anyone else runs into this issue please post it!
All I can recommend at the moment is maybe checking if you have any conflicts between your Graphic Drivers, DirectX etc. Sometimes just updating drivers can correct issues like this. If you've only been using Windows Updates, there's a chance your OpenGL and WebGL drivers could be out of date. Updating those could potentially fix your issue. If you're using a laptop and it's running on LOW PERFORMANCE trying plugging in the power cable and see if that changes anything.
Just lastly, do the FPS issues occur if you enter the game in FREE MODE?