Playing around on my 2nd laptop, which has Solus with both Budgie and MATE installed, but Budgie being primary.
I set up the following config theme:
GTK+ = BlackMATE
Icons = Arc
Cursor = Paper
Here is a screenshot: http://i.imgur.com/hZZMQ1w.png
Now to find out how to install the BlackMATE GTK theme into a single Budgie install, without actually installing MATE, so I could have the setup on my main laptop.