One of the things I miss from Avid in fcpx is the nice big scalable timecode window. This is quite essential when you work in a team where more people need to be able to see the timecode. As far as I know the only solution in fcpx is to add the timecode plugin on your clips and scale that up.
I stumbled upon an Apple app called "Pixie" from the "Graphics Tools for Xcode" which is found on Apples developer site. This app can enlarge a part of your screen and display it in an always on top window.
Just start the app, go to settings and turn off "Enable Development Mode" to get rid of the overlays, scale your window to your size and choose zoom level.
By default it follows the mouse, so just aim at the timecode and lock the axis with CMD+X and CMD+Y. If it gets in the way, just select it and CMD+H to hide it. Or just move it...
The numbers is quite low res from the scaling, but it is probably better on a Retina.
Not a perfect solution, but a good tip I think!