So tonight I did it. I played things conservatively though being that this was my first time going out to a show while tripping since ... way more than a decade.
T+0:00 ~6.5-7 mg 2C-B
T+1:15 ~4.5-5 mg 2C-D
T+2:20 ~4.5-5 mg 2C-D
The 2C-D announced itself at around T+1:30 as a kind of sharpening of the round-fuzzy feelings of the 2C-B. Shortly after, I got a burst of body energy, stimulation, and euphoria. Pronounced time dilation was experienced around T+2:00, which is where the overall effects peaked with some significant tracers and colorful CEVs. The second 2C-D dose did not increase the effects; the window for re-dosing had clearly closed. It did keep things at a pleasant low +2 with plenty of stimulation for the remainder of the event.
Overall I'm very pleased with the result, but except for that rush between T+1:30 and T+2:00, I didn't notice any potentiation. In fact, it was weaker than if I'd taken say 13 mg 2C-B at once or 18 mg 2C-D at once.