I guess my biggest concerns are the response time (don't want ghosting).
As I said, don't rely on the claimed response time. In theory, anything 16ms or lower will be ghosting free. In reality, the claimed response time is meaningless.
And do I lose any top/bottom with this widescreen compared to the fullscreen?
That depends on what you're using it for. In games that are hor +, you don't lose anything from the top or bottom. In games that are vert -, you do.
If the fullscreen is 1600 pixels wide, and the widescreen 1680, is the fullscreen almost as wide as the widescreen?
Try not to use the word "fullscreen" to describe aspect ratio. Strictly by the numbers, the 4:3 screen has 94-95% of the width of the widescreen. But there's more to it than this.