Optimizing OnGUI

Hi. I'm trying to see if it's possible somehow to optimize the OnGUI function in my project. If I make a gui layout label like this:

 GUILayout.Label(PlayerPrefs.GetFloat("Pl1_Score").ToString("N0", new System.Globalization.CultureInfo("sv-SE")), GUILayout.Width(Screen.width / 3.5f));

Then I tell it to get the playerprefs, convert it to string and set the width.

Wouldn't it be better to fill a string like this:

 private String newStringIJustMade = PlayerPrefs.GetFloat("Pl1_Score").ToString("N0", new System.Globalization.CultureInfo("sv-SE"));

and then just write

 GUILayout.Label(newStringIJustMade, GUILayout.Width(Screen.width / 3.5f));

and even better, make the last part a variable as well which you declare in Awake()

 private float GuiWidth;
 GUIWidth = Screen.width / 3.5f;

and writing:

 GUILayout.Label(newStringIJustMade, GUILayout.Width(GUIWidth));

Hopefully that made sense. Would this make any bigger difference?

I have a lot of labels and buttons that work like this and would like to try and optimize it as much as possible. But on the other hand I heard that making a variable in the top of the code is a bad idea and will cause performance issues if you use to many...

Thanks for reading.