That is the highest level estimate I have ever seen for a classical concert, but not too unreasonable when you consider it is peak rather than RMS volume.
As for 160db in rock concerts: that is ludicrously loud. By ludicrously loud, I mean loud enough to have heavy metal concert goers covering their ears and howling. There is no conceivable reason anyone would ever want to produce anything of that amplitude for pleasure. Wikipedia assures me that music never, ever, gets anything like that loud. Even if you did want music that loud, you would push the headphones beyond their mechanical limits in a flash trying to get the volume that high.
The HD650 is worth amplifying (beyond the level of your MP3 player output) to reach dynamic peaks without clipping at reasonable volumes, but it is not an excessively hard to drive headphone. Do the maths, decide how loud you want it to get and choose amplifiers that can provide that much power. A certain NwAvGuy has various charts on his blog which will help you with this: he also uses the HD650 as his example throughout. Have a gander at that and it should give you a good idea.