Can't give you any science, but I use the Bose X and when you turn it on, you can hear it "suck" the noise out of your ears. Also, on the odd occassion I've forgotten it, or lent it to a colleague to try, I can't believe the noise level on the flight deck. Additionally, it makes listening to ATC at lower levels much, much easier.
I was dubious at first, but would absolutely not be without it any more.
Can't rate it highly enough, and if it borke tomorrow, I'd be out to be another one straight away.
DW.
Edited to add: apart from the fact they have a 5 year guarantee, so I guess I'd claim on that first!