It is a standard IFR Takeoff, if you start to lose it check your other enormous AH, what could go wrong?
You could over torque it.
Nil wind, crane ship, humid, Jabba da Hut in the backseat, pitch black
You can still fly into the water with your wings level. I am not taking the piss out of anyone and I would happily do it in a G5 during the day though I personally think I would find certain conditions uncomfortable on departure in a JR that heavy and I wouldn't hesitate to pull a bit more than my qouta to prevent being part of the only S/E SPIFR artificial reef in our waters.
On that note I would think that the guys who have/are doing it must be pretty professional. Very brave and tempting their fate a bit but good IFR pilots