Well your setup is not at 255 quads no 127, and about the other detail, place a character of the normal character size you will see the 1m = 1vertex.
And the memory use turn up when you edit the landscape, you just used an external heightmap.
You sould notice a 4GB of use only in a empty scene with the landscape without textures. And in the images you send 50-60% of CPU use looks like not too normal as you can see.