Sass seemed a bit slow, so just out of curiosity I tried using Less instead.

app.less

@import '../../../bower_components/bootstrap/less/bootstrap.less';

app.scss

@import '../../../bower_components/bootstrap-sass-official/assets/stylesheets/_bootstrap.scss';

gulp-less.txt

luke@samsung:/var/www/test$ time gulp less
[20:58:56] Using gulpfile /var/www/test/gulpfile.js
[20:58:56] Starting 'less'...
[20:58:56] Finished 'less' after 41 ms
[20:58:59] gulp-notify: [Gulp notification] less task complete

real    0m11.752s
user    0m11.244s
sys 0m0.599s

gulp-ruby-sass.txt

luke@samsung:/var/www/test$ time gulp sass
[20:58:29] Using gulpfile /var/www/test/gulpfile.js
[20:58:29] Starting 'sass'...
[20:58:29] Finished 'sass' after 46 ms
[20:58:30] gulp-ruby-sass: directory
[20:58:41] gulp-ruby-sass: write app.css
      write app.css.map
[20:58:42] gulp-notify: [Gulp notification] sass task complete
[20:58:42] gulp-notify: [Gulp notification] sass task complete

real    0m21.199s
user    0m20.381s
sys 0m0.744s

gulpfile.js

var gulp = require('gulp'),
    less = require('gulp-less'),
    sass = require('gulp-ruby-sass'),
    minifycss = require('gulp-minify-css'),
    rename = require('gulp-rename'),
    notify = require('gulp-notify');



/*
    Convert SASS to CSS and minify.
*/
gulp.task('sass', function() {
    gulp.src('resources/assets/sass/app.scss')
        .pipe(sass())
        .pipe(gulp.dest('public/css'))
        .pipe(rename({suffix: '.min'}))
        .pipe(minifycss())
        .pipe(gulp.dest('public/css'))
        .pipe(notify({ message: 'sass task complete' }));
});


/*
    Convert LESS to CSS and minify.
*/
gulp.task('less', function () {
    gulp.src('resources/assets/less/app.less')
        .pipe(less({}))
        .pipe(gulp.dest('public/less'))
        .pipe(rename({suffix: '.min'}))
        .pipe(minifycss())
        .pipe(gulp.dest('public/less'))
        .pipe(notify({ message: 'less task complete' }));
});