I'd like to suggest "overall mitred tube lengths" (if they aren't already in there!!) as a set dimension.
It would be great to have that set as a standard dimensions. I could select them for a Template so I could see at a glance if my standard tubes are long enough.
I had a look and don't think there is a option of "overall length" Dimension for a mitred down, top or seat-tubes. For a frame I'm working on, a "Start Linear Dimension" measurement from the Side of the down-tube at the Head-tube, to the Tip of the down-tube beneath the BB shell, is 4mm short of the un-mitred tube.
Just to clarify, I assume you are looking for a dimension like the one below:
Unfortunately, that is not currently available as a default dimension. That's a good idea though and I will try to add that to a future update. In the meantime, creating a user dimension as you have done would be a good solution.