It depends on what you are rendering.

Let us say you are rendering a face. The face has a texture map of 4000x4000.

The size of your entire image is 2048x2048, and the face takes up half of the image, you could drop that texture map down to 1024x1024 without losing too much detail.

In other words, if your entire image is 2048x2048, you have just over 4 million pixels. Your image map has 160 million. So there is no way that 160 million pixels will fit into 4 million pixels.

When you reduce your texture map, use the following sizes:
512x512 or 1024x1024 or 2048x2048.

The PC will render images in the sizes more efficiently than say an image of 2000x2000, because those size work better with the internal calculator of the render engine.

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