Not sure what you mean by the second question. How big is the image? What's it a picture of? If it's meant to repeat, it should be made as small as possible: generally just one iteration each way.
It's not a picture. It's a gradient background image. I was mistaken when I wrote use repeat-x, I meant repeat-y. It theoretically can be 1px high, but it needs to be 1140px wide because of the direction in which it is a gradient.