I have a pair of SRH750DJ, which aren't quite good enough for the 8.5 hour flight I'll be taking at the end of the week. I know this because they weren't enough when I took an 8-hour flight at the beginning of the week. I've also tried SRH440's and found the noise cancellation to be only on the order of 1-2dB difference compatred to the SRH750DJ. It still isn't enough for a long flight with lots of airplane noise and chatting passengers.
I've tried Bose QC15's in a store and found that they made a very high pitched sound, which was irritating, if that's at all helpful to anyone making suggestions.