Here's one datapoint, from building the single JS entrypoint for this simple demo site: https://exogen.github.io/layup/

First build:

    Parcel:    23.9s, 422K output size
    webpack 4:  9.6s, 399K output size

Rebuild (cached, no changes):

    Parcel:     900ms
    webpack 4: 1400ms

Do you have experience with using parcel in production? How is it? On a previous project, our webpack bundle could take up to 20+ seconds - but we love the customizability that comes with webpack.