PHTR,
Unfortunately I've never used the Bose so I can't compare.
I can compare with the DC X11's - I was about to buy a set, borrowed a mates and used them in a Beaver - I was very disappointed and when I swapped in flight between them (even with the ANR on) and some passive DC's (10-20's I think) and I honestly couldn't say if they were any quieter. The Telex are a different story, in the DHC-2 they take out most of the engine noise including the supercharger howl leaving mainly high frequency wind noise.
After a day in the Beaver now my hearing appears to be unaffected, unlike when using passive headsets when I can definintely notice some effects. I was a bit apprehensive when I ordered the D50's without trying them on or speaking to people who had used them (they were recomended by a number of pilots on the DHC-2 forum), but I would definitely buy another set again. Some of the other guys at work have tried them and they were very impressed too.
W