Quote - Any chance that the dimensions of the preview window could be explicitly set even when it is docked (perhaps an option). 

As it is, it sizes to fit the available space, which is good, but I'd like the option to set it to a specific resolution but also keep it docked (so that I don't have the window dialogue edges) since it looks nicer.

An option to toggle between specific size and fit to space would be appreciated.

That's sort of there already. Press Ctrl-Alt-D and set the render dimensions

The preview will show a highlighted box that is the same aspect ratio, but scaled to fit the preview window size. This way you get the same render no matter the window size/layout, and also you can compose effectively because the area that will be rendered is highlighted.

EDITED: I wrote the wrong keystroke  - it is Ctrl-Alt-D not Shift-Alt-D

---

Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)