Sounds serious, when I hear you describe how much soot she's coughing out I fear that driving WOT at top speed on long stretches isn't healthy ! Exhaust temperatures risk being much to high cooking the turbo, exhaust valves and head gaskets...
White smoke could indicate that coolant found it's way past the head gasket into the combustion chambers.
Give it a tiny sniff of start pilot in the air filter to get it running (tiny bits at a time, isn't all that healthy for diesels, when she starts and revs up cut the engine, after that you will get her started normally). Look for bubbles in the expansion tank while engine is running. Check oil for water contamination.
I hope you get her running allright soon