Gtoolkit [1] is a cutting-edge example of what's possible. I say "cutting edge" because it relies upon a dev version of Bloc, which is the new graphics system being developed for future versions of Pharo.

Any sluggishness you experience with Gtoolkit, by the way, is because Bloc is being hosted in Morphic (the current graphics system) temporarily.

[1] http://gtoolkit.com