Sass @for over list

gistfile1.scss

@mixin header($size) {
  font-size: $size;
  line-height: $size;
  @include breakpoint($small) { font-size: 1.125 * $size; }
}

$header-sizes: $h1-font-size,
               $h2-font-size,
               $h3-font-size,
               $h4-font-size,
               $h5-font-size,
               $h6-font-size;

@for $i from 1 through 6 {
  h#{$i} {
    @include header( nth($header-sizes, $i) );
  }
}

h1, h2, h4, h5, h6 {
  color: $orange;
  margin: 0;
  font-family: $montserrat;
  font-weight: bold;
}

h1, h2, h4 { text-transform: uppercase; }