解像度によってGUITextureの大きさを変更するサンプル

NotPixelperfectGUITexture.cs

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
[RequireComponent(typeof(GUITexture))]
public class NotPixelperfectGUITexture : MonoBehaviour
{
  [SerializeField]
	Vector2 screenSize = new Vector2 (800, 1280);

	[SerializeField]
	Rect pixelInset ;
	
	void Start ()
	{
		if (pixelInset.Equals (new Rect (0, 0, 0, 0))) {
			pixelInset = guiTexture.pixelInset;
		}
	}
	
	void Update ()
	{
		float x = Screen.width / screenSize.x;
		float y = Screen.height / screenSize.y;
		
		guiTexture.pixelInset = new Rect (pixelInset.x * x, pixelInset.y * y, pixelInset.width * x, pixelInset.height * y);
	}
}