I was going to use cobalt bits, any good?
Its the turbo mounting studs that have snapped off, to close to use extractors, and due to the heat cycles these go through I'm guessing they will be uber hard?
Any recommendation gratefully recieved...........

 

Not quite the same but i drilled out a mates set of pug locking wheel nuts with black & decker titanium bits with good results.
Believe it or not the best results i had before the titanium bits were masonory bits with slow speed and plenty of tuff cut lube !!!! had to sharpen them twice but went right through with very little effort.