In a new blog post are details on Hawaii memory usage. With the Hawaii 0.2.0 release being imminent, the RAM usage between Hawaii and Xfce was compared.
Comparing application memory usage is terribly hard to produce meaningful data, but their results show that Hawaii on Weston is consuming a total of 87MB of RAM while the Xfce stack on an X.Org Server is consuming 154MB. Of those amounts, 9MB is used by Weston with Hawaii while the X.Org Server and the xfwm4 window manager alone are consuming 123MB of Xfce's memory amount.
Unfortunately there aren't Hawaii X.Org vs. Wayland/Weston numbers to compare the Wayland memory usage directly. Likewise, there isn't yet a proper Xfce port to Wayland as the lightweight desktop is still largely reliant upon GTK2 (though there's been some GTK3 progress with the yet-to-be-released Xfce 4.12). Also, Hawaii is still using Weston as its compositor but the project is developing Green Island, a Qt Quick compositor using the Qt Compositor interfaces with Wayland.
Those wishing to read more into these memory usage metrics can read the blog post.