for my own HUD I used this method as i had imported quite a few of my own fonts and was using lots of different fonts.

I imported my desired font and changed the size of that specific font in the inspector (for me I changed it from 16 to 40)

I then added a variable

MyFont

or whatever you want and choose the font you want

you then add the line

GUI.skin.font = MyFont;

before each label that you want to have a different font

var MyFont : Font;

function OnGUI () {
GUI.skin.font = MyFont;
GUI.Label(Rect(10,10,200,30), "You survived " +totaltime + " Seconds");
}

you need to define a GUISkin/GUIStyle to replace the font. And you can change the font size by double clicking it and then you'll see Font size in your inspector.