title: Improve performance of webpack's CSS compilation
body: <p>I'm trying to move our SASS build from gulp + node-sass to webpack with the sass-loader.</p>
  
  <p>As a reference point, gulp + node-sass 3.2 gives us roughly 2.5-3 second build time.</p>
  
  <p>In webpack, if I use style!raw!sass for loading, I'm looking at 10~ second build, and no sourcemaps (because of the raw loader). If I put the css loader for sourcemaps to work,  the additional parsing makes the build take 20-30 seconds on a good day.</p>
  
  <p>I'm wondering what tricks I can use to improve things. Right now the best I've been able to do is split our sass compilation by having a lot of require(...) from javascript to SASS, which then get concatenated in one file. With -watch option, that allows for some a faux-incremental compile, so after the initial build, it isn't too bad.</p>
  
  <p>I'm wondering if there's something I can do beyond that to make it better. 10x slowdown over gulp + nodesass isn't great, but having 2 build tools isn't great either (webpack works 100% fine for JS, even with massive amount of code)</p>