I'm often confused by this. I've always been taught to name numbers I use often using variables or constants, but if it reduces the efficiency of the program, should I still do it? Heres an example:

private int CenterText(Font font, PrintPageEventArgs e, string text)
    {
        int recieptCenter = 125;
        int stringLength = Convert.ToInt32(e.Graphics.MeasureString(text, font));
        return recieptCenter - stringLength / 2;
    }

The above code is using named variables, but runs slower then this code:

private int CenterText(Font font, PrintPageEventArgs e, string text)
    {
        return 125 - Convert.ToInt32(e.Graphics.MeasureString(text, font) / 2);
    }

In this example, the difference in execution time is minimal, but what about in larger blocks of code?