Question about resolution and monitor size

Anyway, I bought a monitor 27-inch, 2560x1440 resolution, but that resolution fps drops, we have to reduce the graphics to medium (the gtx 1080).
The hardware is all so, works as it should, I just need more fps.

And so the main question.
If you take a full hd monitor, 27 inches, it will look the same as mine changed to full hd?
I have icons increase and looks very soapy, it is all one 27 inch full hd monitor?

Please answer the questions above, I know how to change the resolution, I know that you can expect to lower...