Firefly,
Not quite sure what you mean by a speed for tail rotor failure ? But as you say there are different kinds of emergency: stuck pedals, control failure or fenestrom failure.
As B Sousa says, it appears that if you are not in the hover, ie making translational flight, then Eurocopter manual requires you to auto in all these emegencies. Squirrel however does permit you to do a run on landing if you have only tail rotor CONTROL failure.
I've 2000 hours on helis and 1400 instruction from 22 to 407. I don't instruct on the EC because I have only about 25 hours on it and don't feel comfortable with these sorts of issues and particularly the risk of hot starting it while training, especially as it is not covered by the insurance anymore. That discomfort with the EC is amplified when it's suggested that things might be different with a fenstrom and it makes me feel like I don't know the whole story.... I have tried to go on the Eurocopter ground course recently but they changed the dates at the last minute and I couldn't make it.
Maybe someone with fenestrom experience would care to comment ?