I still think that dump valve induced overspeed is potentially as bad as, if not worse than, compressor stall so the jury is out in my mind, although i DO know of GT turbos letting go immediately after a throttle off with both:

Dumper fitted....
Dumper not fitted....

No help whatsoever in that case...roflol

For smaller turbos im happy to recommend no dump valve at all if your not bothered about the sound you will have to endure/enjoy.